Common Infected

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Common Infected
Health	30/50/50/90 (Easy/Normal/Adv./Expert)
Abilities	Climbing walls, Breaking doors
Attacks	Punching, clawing, kicking.

"I'm not gonna let these goddamn vampires beat me."

—Francis

"They're zombies, Francis."

—Bill/Louis

Common Infected are the most commonly-faced members of the Infected, and the easiest to defeat. Their strength lies in the fact that they attack in groups, more commonly referred to as the Horde, sometimes as large as several dozen. While they seem capable of ignoring pain, they can still be killed as easily as any normal human can. They are capable of climbing ladders and scaling objects once they find a target, and will not stop until it is dead. The default number of Infected that are spawned in a horde is around 30. These Infected are fast, sensitive to loud noises and movement, and able to attack in ravenous waves, as determined by the Director. They might not notice you right away, but when they do, watch out—they're fast, and it won't take long for them to close the distance.

Contents 1 Meet the Horde 1.1 Appearances and Action 1.2 Extent of Mutations 2 Tactics and Tips 2.1 Closet mode 2.2 Remove Loners 2.3 Weapon of choice 2.4 Power of the Horde 2.5 Darkness is your Friend 2.6 Playing smart 2.7 Infected tips 3 Uncommon Infected 3.1 Infected CEDA Workers 3.2 Clown Infected 3.3 Mud Men 3.4 Worker Infected 3.5 Riot Infected 3.6 Jimmy Gibbs Junior 3.7 8th Common Infected 3.8 Fallen Survivor 3.9 "The Passing" Uncommon Common 4 Trivia 5 Gallery 6 References

[edit] Meet the Horde

The "Horde" is a term often used as a reference to a medium to large amount of Common Infected. A Horde can be powerful but they are not invincible by any means. These Hordes can often be distracted very easily in many ways. For example, Common Infected are drawn to loud noises and bright lights. Also, they can be startled by simply shooting an alarmed car, which summons a massive Horde of Infected. There are several times throughout the campaigns where the Survivors are forced to do something to alert the Horde in order to proceed to the next segment of that chapter, such as opening an emergency door that will set off an alarm or turning on a noisy generator. And, there are other times, as mentioned before, where the Survivors may accidentally alert them by setting off a car alarm or metal detector, or if Re: Your Brains starts to play on a jukebox. All of these trigger something called a Panic Event, which causes a large Horde to spawn and attack you. When a pipe bomb is thrown, all of the Common Infected in the immediate area will come to investigate the loud beeps and flashing lights, chasing after the pipe bomb and clustering around it until it explodes, killing them. When Common Infected attack from the front, they do approximately 1 damage on easy, 2 on normal, 5 on advanced and 20 on expert. If you are hit in the back, they do 0.5 damage on easy, 1 on normal, 2.5 on advanced, and 10 on expert.

[edit] Appearances and Action

Common Infected come in variety of appearances, both male and female. They are the victims of the vicious virus only known as The Infection that is sweeping through the area. The infection is apparently transmitted via bites from other Infected.

Common Infected do not differ in appearance from a healthy human as much as Special Infected do. According to the game commentary, the developers designed multiple types of faces and bodies, and would have the computer pair them when spawning Infected, ensuring a variety of characters. This allows for "something around 1500 possibilities". Some Infected models can be seen in any scenario of the game, while others, such as the Infected patients in Mercy Hospital or airport custom officers in Dead Air, are only encountered at certain areas.

When not attacking, they are very vulnerable, usually sitting down, leaning on walls, or simply standing. Usually, when in this state, a Common Infected can easily be taken down instantly by a shove or melee attack; they must be unaware of your presence. They are easily provoked by light, sound, or touch, but are normally only dangerous in large groups or when completely surrounding a player. The heads, arms and legs can all be shot or cut off, this happening easiest using a powerful gun or a slicing melee weapon. The Infected react naturally to gunfire in their vicinity, turning towards the sound to attack the shooter. Shooting one in the foot will cause a very different reaction than shooting one in the chest with a pump shotgun. Usually, if an idle Common Infected receives a non-fatal gunshot wound from a distance they will writhe in pain and clutch the wound with their hands, but if they are running towards the player and receive a non-fatal gunshot wound they will just continue to pursue the player and ignore the pain. This can be most easily observed by shooting them with a pistol. They are often seen engaging in bizarre activities (e.g. vomiting, attacking inanimate objects, fighting each other) when unaware of the Survivors, but begin to rush at the Survivors the very moment they see them. A Common Infected's attack slows down the target player, making it exceedingly difficult to run away from a mob of them that is close to you. They also seem to be at least smart enough to attempt to trap the player, commonly running ahead of him or her and attacking from in front to prevent movement, assuming there is also a horde behind the player.

The Infected appear to lack a sense of self preservation, as they will actively charge into flames, explosions, off of high buildings, and against superior forces of the Survivors and their weapons, even if they have encountered these things before. A possibility is that the Infection has affected their brains to such a degree that they only think of spreading it, or may simply think of attacking anything that wakes them from their stupor. The Infected also are not known to feed or drink, as in the first level of Dead Air, there is a piece of graffiti that says "They don't eat, they don't sleep, what keeps them going?", and it is possible that the Infection has removed the mental ability to perform these necessary life functions. This may indicate that the Infected may eventually die of starvation or dehydration, and possibly even exposure to the elements as the Infected do not seem to seek shelter in conditions that non-Infected would (the theme of the Infected dying out and repopulation commencing is similar to what happened following the events of the film 28 Days Later). However, it's possible that the Infected resort to cannibalism, as evident from the blood on their mouths. It is also possible that the Infected just bleed from their mouths. Common Infected's hair and skin pigmentation is usually very low, resulting in pale skin, and sometimes pale hair. Some Infected, such as Boomers, Smokers, and other Commons may have black or dark hair. The Infected appear to be capable of many acrobatic actions, such as climbing fences, climbing walls and many other actions to get at Survivors.

[edit] Extent of Mutations

Though the Common Infected have evidently been mutated the least physically by this strain of the infection, the strain appears to have had a bigger effect on their minds. It seems that they have lost many of their higher brain functions, as they seem to be distracted easily by loud noises and flashing lights, and lack a sense of self-preservation, essentially making them mindless cannon fodder to a certain degree. However, their sense of smell and hearing have been greatly enhanced, possibly explaining things such as Crescendo Events and how the Infected are able to notice the Survivors from the littlest things such as the Boomer bile. It's possible they've had very slight boosts in strength, speed, and endurance—though, again, it appears to be slight, as they don't withstand many bullets or hits in general, or due to loss of higher brain functions, they seem to ignore pain and damage. They also tend to be incredibly hostile to anything not perceived as being Infected, though there are occasions when two Infected are seen fighting one another, maybe because the infection causes both aggressive and passive behavior. Overall, they seem quite animalistic in nature.

The Common Infected seem to no longer be able to speak coherent language, instead shouting gibberish and screaming at Survivors. However, they have been perceived as saying things, though this is probably more a trick of the mind than anything. Some people have heard them saying things such as "let us inside" while in a safe house, or a slightly stranger "I think I might blow a head gasket!" Others have heard them uttering things like "buenos dias", which is Spanish for "good morning". It's possible they are trying to verbally communicate to some degree, though it's slightly irrational as they seem to do more talking with their bodies than anything. It's also possible that, much like the Headcrab Zombies of Half-Life 2 (who often screamed things like "Oh, God, help me!" in reverse), these are actually phrases which have been sped up and/or reversed.

If nothing else, they seem to have some grasp of their current situation, or at least how they feel; generally, idle Infected act physically ill, holding their heads and vomiting as they shuffle around slowly. Occasionally, if you watch one long enough, one of the Infected who is holding their head may begin to writhe in pain, or they may simply lie down and sometimes die without being shot or punched, suggesting that the virus is deadlier than it seems. It is also possible that after Infection, they have a limited life span, just like how people Infected with rabies (The virus the game's virus was based on) have a limited lifespan if left untreated. It could also be through brain hemorrhaging, as Infected appear to bleed out the ears. This also explains why they hold their heads in pain. Another possibility is that these deaths may be the result of an injury that the Infected person received earlier, such as from a gunshot from other Survivors or from a fall that they endured.

[edit] Tactics and Tips

Common Infected are only strong in numbers. Sticking together is key to keeping them off you and your teammates' backs. If you are concerned about conserving ammunition, consider using the pistol, which kills them in just a few shots or in one head shot on any difficulty, not to mention it has infinite ammo.

[edit] Closet mode

When a horde is about to attack, the best tactic is to back into a corner (preferably) or a wall. Assign the front two Survivors to crouch and melee continuously while the two Survivors behind them stand and fire their weapons at them. This works equally well when Survivors have been covered in Boomer bile. Finding the nearest door, closing it, and using a shotgun to blow out a significant chunk of it provides you with a shield that you can see through, as well as keeping the Infected from touching you—very useful for higher difficulties. The most important thing is limiting the area the Common Infected have to attack from. You may also throw a pipe bomb to divert the infected once you have been covered in Boomer bile

Note: This is not recommended for Left 4 Dead 2. This is because the A.I. director will eventually spawn a Spitter that will force you away from your position. Ultimately, this will bring you out into the open, possibly surrounding the player with even more zombies. Also, L4D2 has implemented a fatigue timer which will force a three-second pause after 5 rapidly consecutive melee hits, and then after every hit until a 'cooldown' has been taken. The cooldown usually lasts anywhere from one to three seconds.

[edit] Remove Loners

Pick off lone Infected that have strayed away from fellow Infected whenever you can. When entering a new area, swap to pistols or snipe via a hunting rifle and take out as many lone Infected as you can from the entryway as long as it stays quiet. The Director has a tendency to spawn hordes once you reach the mid-point of areas, and this "event" will cause any idle Infected in the area to attack as well. In Versus, however, it is unlikely the Special Infected will allow you to sit in one place long enough to clear a room in this manner, so keep moving.

NOTE: You could alternatively throw a Molotov cocktail to set fire to remaining infected in the room.

[edit] Weapon of choice

All weapons possess the ability to fire through multiple Infected, therefore positioning yourself so that the Infected are funneled into lines is effective.

Any shotgun can be very useful against the horde, as their shells deal large amounts of damage and can pass through multiple Infected. The auto shotgun/combat shotgun are slightly superior as shotguns go, as they can decimate groups in mere seconds, and there is no pause to pump the gun. A good tactic to use if they are coming through one area, such as a doorway, is to keep your fire pointed at the entry, as the Infected will be clustering together to get through, making them easier to kill. Remember to push the zombies back while reloading simultaneously taking into fact that the shotgun will take much longer to reload than any automatic weapons.

As far as Automatic Weapons go, the assault rifles can do major damage at any range. The Combat Rifle excels mostly at range fighting and ammo conserving, but when a horde is in a player's personal space, it will lack the automatic fire and power to dispatch the infected quickly. The AK-47 is the opposite; while it is poor at best at taking out distant enemies, its high power and low accuracy spread can clear out infected in close range. As for the Assault Rifle, its a medium grade in between both the Combat Rifle and the AK-47, it has a decent power and long range, fully automatic and good accuracy.

Given the Hunting Rifle or the Sniper Rifle, both should only be used to kill distant infected. In a pinch, they can be used to kill attacking infected with their high rate of fire. However, the rifles do excel at one thing: bullet penetration. If multiple infected are being funneled through a tight area or are otherwise "stacked" (like when climbing an obstacle), the rifle family can shoot through multiple infected in a single bullet.

[edit] Power of the Horde

The Common Infected are especially dangerous on the expert difficulty. It can only take a couple of hits to down a Survivor, depending on the Survivor's current health. On this mode, the Common Infected also deal much more damage: 20 for each hit on the front, and 10 for each hit on the back. This means a Horde can easily cripple an entire team if they do not pay attention. The Infected often run up behind Survivors and hit them in the back, downing them before they can realize that they are being attacked. To avoid this, constantly watch behind you and look for Infected sneaking up behind your teammates, but do not shoot when they are close to Survivors to avoid friendly-fire. Instead, Melee them off, and then shoot. A good tactic is to always have someone watching behind the group. Communication is also key; always tell other Survivors when they are in danger. Also, it might be a good idea to hop on top of a car or van that has no alarm set because higher ground is usually recommended for fighting large amounts of Infected. Horde attacks also slow down players, if they do not communicate this to other players, they can easily be left behind.

[edit] Darkness is your Friend

The Common Infected are obviously known to be attracted by the noise of car alarms and other loud sounds caused by most Crescendo Events, however, most have not realized the flashlight can also enrage Infected. Its effect is similar to that of a pipe bomb, as the bright, flashy lights irritate them, drawing their attention to the player. Using this knowledge may help if two of the Survivors have their flashlights on while the others do not, causing the two "aggro men" to become focused on while their partners are able to break off the rest of the Infected.

[edit] Playing smart

Common Infected are only a real threat in great numbers, but the Director likes to mess with the Survivors, especially when everybody is low on health and close to a safe room. If this does happen, you can more than likely expect one last horde to come at you; therefore, throwing a pipe bomb can mean the difference from barely limping to safety, and starting all over. The Director will sometimes have Common Infected standing right against the safe room door in higher difficulties. Be careful! as the horde usually hide a special infected or act as a decoy or a frustration, such as if the Tank is attacking the common infected will slow you down or make you waste your ammo instead of using it on the tank.

[edit] Infected tips

When playing as the Infected in versus, you can use the Common Infected to your advantage. While the Survivors are attempting to reach the safe room, there are many ways you can exploit the Horde. Once the Survivors are occupied by the Horde, a competent Tank can defeat even the most organized Survivor team. Boomers can not only summon the Horde but also "extend" it by vomiting on the Survivors after they have dealt with the present Horde. Smokers are also effective during Horde as they can snatch a Survivor and pull them away whilst the others are too busy fighting to help. Smokers can also be protected by the Common Infected. If you have snared a Survivor and you pull him in front of you where you can hit him, the Horde will attack along with you, killing them faster. This circle of Infected makes it harder for the Survivors to kill you. You can even do a substantial amount of damage with a Hunter before the Survivors can deal with the Horde and kill him. Other Infected will also surround the Hunter to claw at the Survivor. There are around 30 Common Infected within a Horde. During a Horde attack is the best time to work together, Special Infected need to cooperate and doing so with the Common Infected can be fatal to the Survivors.

[edit] Uncommon Infected

The Uncommon Common, the Uncommon Infected, or simply the Uncommon are new forms of the Common Infected introduced in Left 4 Dead 2. They have the same general weaknesses and health as most Common Infected, but there are a few differences that can affect how they're dealt with. Every campaign has its own unique Uncommon Infected, with the exception being Dead Center, which has two.

[edit] Infected CEDA Workers

"Are those guys fireproof?!"

—Nick

The CEDA Worker Infected was the first Uncommon Common to be announced and appear in the Left 4 Dead 2 campaign, Dead Center. Players will occasionally come across Common Infected wearing a hazmat suit, which was worn prior to the person being Infected. When killed, there is a chance of them dropping a Bile Bomb (in which case it will be seen strapped to their side). Upon death, the sound of air hissing out of their now punctured hazmat suit can sometimes be heard. This would mean the hazmat suit was not punctured since the person became Infected, it is thought that the person must have been bitten before they suited up. This may also indicate that the infection is indeed airborne and got inside the suit while the wearer was getting suited up. Through development of Left 4 Dead 2, the campaign the CEDA Worker Infected appeared in changed from The Parish, to extend to Dead Center, to being removed from The Parish completely, they are being replaced by the Riot Cop.

Though not as numerous as normal Common Infected, they share the same health, abilities and weaknesses. However, due to their hazmat suits, they do not burst into flame, and are resistant to fire. If idle within fire for extended periods of time, they will die due to the heat. They come in two different varieties: yellow suits and green suits. There were also white suits, but these were only seen in the "Survival" trailer or spotted as ragdolls scattered about certain areas including the Parish.

[edit] Clown Infected

"Shut that clown up!"

—Ellis

"That squeaking is driving the zombies crazy!"

—Nick

Once a lovable comedian, the Clown Infected is now a victim of the spreading infection. They wander around the Dark Carnival campaign and when they spot Survivors they will charge, calling other Infected in with their noisy, squeaky shoes for an attack. (This does not actually spawn any new Common Infected. It only attracts idle Common Infected nearby.) Any melee attack can honk the clowns nose, if done 10 times the player shall be awarded the "Cl0wned" achievement. Clowns pants come in a different types of colors some include red and white blue and white and pink and green as seen in the picture and a couple of others.

[edit] Mud Men

"Mudder!"

—Nick

The Mud Men appear in the campaign Swamp Fever. They are similar to the Common Infected, except that they are covered in mud and use this as camouflage. Mud men sprint on all fours, although stumble back on two feet when shoved. They also run faster than Common Infected and are not slowed down by water. A hit from a Mud Man obscures the players screen with mud. This increases with successive hits, blurring the screen in a way similar to Boomer Bile. The Mud man's movement can actually be observed in Left 4 Dead. If a player enters an area that requires them to crouch, the Infected will follow them in, but instead of crouching, they will in fact crawl on all fours to get to the Survivor.

[edit] Worker Infected

When this unfortunate demolition crew receives orders to tear down an old sugar mill, they instead became Infected. Dubbed Worker Infected, these Infected populate the Hard Rain campaign. Workers are equipped with ear protection, hardhats, and reflective vests making them easier to spot in the downpour. Their earmuffs make them unable to hear Pipe Bombs, and their blunt melee resistance is greater than usual. (They also seem to be immune to bile bombs when Infected are not covered, since the bile alone on the ground uses the same attention-drawing programming as the pipe bomb, a rather large oversight. They will be drawn to attack bile-coated Infected, still, but will re-target the Survivors once the affected Infected are dead.) Another great hindrance is how similar they appear to the Spitter from a distance. Inexperienced players might have a difficult time trying to find a Spitter in a horde with Worker Infected present. They are also the only Uncommon Common to appear on every chapter of its campaign (The other four missing in either the first or last chapter of their respective campaigns.)

[edit] Riot Infected

"Ah hell! Now they're bulletproof?"

—Ellis

"That zombie's got armor! I want armor!"

—Coach

The Riot Infected appear in The Parish campaign. While human, they were members of a private security firm hired by CEDA to protect civilians. They became Infected whilst wearing their armor. This gives them immunity to bullets and resistance to melee from the front, but not from behind; they are still harmed by fire. Dead Riot Infected may drop a Nightstick or a pistol. Riot Infected were first featured in the demo and were part of the censorship controversy in Australia due to rules regarding violence against authority figures though they still appear in the full Australian game. They do not, along with the Worker Infected, have an Achievement linked to it (Dead in the Water for Mudmen, Robbed Zombie for the CEDA workers and CL0WND for the Clown Infected). They breifly apear in the zombie survival guide trailer.

[edit] Jimmy Gibbs Junior

"If the laws of nature allowed it, I would bear that man's children."

—Ellis

Jimmy Gibbs Junior is a "famous" racecar driver from the South. He is dressed in his racing suit and spawns, albeit very rarely, in the Atrium. He is mentioned by the Survivors briefly, saying things such as "If we see him, someone else is going to have to kill him", and Coach is known to occasionally call out "Hey! Jimmy Gibbs!" during the scramble for gasoline, even if the racer is not present. This may be another play on the movie Dawn of the Dead, where the Survivors could see Infected versions of famous people that they knew from the mall. He has 1000 HP, no detachable limbs, can blind the player with motor oil (similar to the Mud Men's splatter effect) is not drawn to pipe or bile-bombs and thanks to his racing suit, is nearly fireproof. He can be spawned with a console command.

[edit] 8th Common Infected

This new Uncommon Infected is set to appear in the upcoming downloadable content campaign, "The Passing". It is currently unknown what it may be. There is some speculation that the new Uncommon Infected will be an edited Fallen Survivor.

[edit] Fallen Survivor

The Fallen Survivor was evidently a fairly well-equipped Survivor from the initial outbreak, but unfortunately became Infected later on. He wears militia attire including a boonie cover and three ammo belts with a strap carrying visible molotov, pipe bomb and pills. He also has a first aid kit and a magnum pistol in a holster strapped to his right thigh. His ability was that he would immediately ignite if shot, due to the molotov that he is carrying and deal large amounts of damage to the Survivor. Melee weapons were useless against him because they also would ignite the molotov. Also, he might drop Health Kits that you could actually put into your fourth slot, and you would have had to carry it like a Propane Tank to heal yourself. Your primary weapon disappears, and the health kit is invisible.

The problem was that the Boomer already held the title of the "explosive" Infected. He was cut from the final game for being too overpowered if killed in a horde. There is a possibility of him being cut due to his ability being extremely dangerous to the Infected as well. He can be seenhere, with mods. Interestingly enough, his character model is nearly identical to that of Whitaker. He can also be seen briefly in the "Zombie Survival Guide". Also like the Jimmy Gibbs Jr. Infected, he can also be spawned by a console command.

[edit] "The Passing" Uncommon Common

The New Left 4 Dead 2 DLC "The Passing" was revealed to have a new uncommon common infected. Nothing is known about it. It might possibly be the "Fallen Survivor" uncommon common that was hidden in the Model files.

[edit] Trivia

• It should be noted that the Common Infected bear a resemblance to the "zombies" in the movie 28 Days Later, as they are not the undead monsters of traditional zombie culture but living people Infected with a rabies-like virus.
• Children and animals have yet to be seen in the ranks of the Infected. It is possible that The Infection is too strong for children and animals, so they die instead of turning into Infected. The most likely explanation is that the censoring of content in some countries prevents media from showing children from being harmed. Rather than make different games for different countries, it's easier to just leave out "unsavory" content. It is unclear why animals are never seen, but the most likely fact is that rabid animals just aren't as horrifying as infected humans, or that humans are more emphatic toward animals. Other possible in-world explanations could be the Infected have either killed most of them or given them a deep seated fear of humans and as such all animals now avoid civilization and human paths. They aren't seen in Blood Harvest simply because human activity in the area recently increased, so they are avoiding it. However, in Blood Harvest, Dark Carnival, and Swamp Fever dead cows can be seen with the skin removed around their face, indicating a rabies test. The lack of the bodies of children could also be that any Survivors saw it appropriate to take the time and give children an appropriate burial, or that they are just removed from sight to not demoralize people. It could also be due to memory limitations; Common Infected use either a male or female template and a randomized appearance selected from a few texture sheets. Children and animals would require extra templates and textures, using up more memory. Animals, in particular if done in this fashion, would require many different templates, for a variety of animals, and a lot more textures.
• In the Zombie Survival Trailer dogs are heard barking.
• Sometimes, a glitch occurs where Infected are standing stationary with their arms parallel at 90º, these Infected can be killed but ragdoll physics do not take effect. Also these glitched Infected can stop Survivors from moving and so it has been seen that Survivors can be trapped by these glitched Infected. To combat this you must restart the server upon which you are playing, or use explosive measures to get past them.
• A second glitch can occur when one tosses a pipe bomb, such as throwing one towards a horde, and occasionally some Infected may stop moving and glide back and forth, but you are still capable of killing them.
• Sometimes, Common Infected can get stuck in objects, such as tables or forklifts, and become invulnerable to melee attacks and must be shot to be killed.
• Found in the sound folder are clips titled to be belonging to a sort of Infected Dog. This could possibly have been a scrapped feature or plans for a future addition. During the 4th chapter of Blood Harvest, it should be noted that howling can be heard in the background, most likely produced from these sound files. However, there is a strong possibility that the file could have simply been applied to the various ambiance that can be heard throughout the campaigns made by idle Infected.
• The voices and sounds of all the Common Infected and Special Infected (with the exception of the Tank, Witch, Charger, and Female Boomer) were performed by vocalist Mike Patton; additional voices were voiced by Fred Tatasciore.
• One of the Infected screams can be identified as one of the GLaDOS AI Component death sounds when you drop one of them into the incinerator in Portal. This is probably Valve reusing sounds in their games, as they reuse several other elements from their past games.
  • This is due to the fact that Mike Patton did the voices for both the Anger Sphere and some of the Infected in Left 4 Dead.
• It is possible to kill a Common Infected simply by jumping on their heads. To do so, simply walk off an edge which is at least a little taller than the Common Infected, and onto their head. This will instantly kill the poor soul.
• It is possible that the Infected have grown smarter in the time between Left 4 Dead and Left 4 Dead 2. In the announcement trailer the Infected can be seen running from an explosion. However, it could be that the zombies are just chasing something at the time.
• When the Infected are summoned in the finales you hear a scream from them. That sound is a mix of two sounds that can be found in the Half-Life sound folder called "the_horror1" and "the_horror2".
• Common Infected can be instantly killed with a melee in the back, earning the player the "Spinal Tap" achievement.
• It is worth mentioning that the Infected running towards Coach in the GameStop Pre-Order trailer is a Mud Man, therefore, it should have sprinted on all fours rather than just running, besides the fact that there are no mud men in Dark Carnival.
• Whenever Common Infected are burned in Left 4 Dead 2 (excluding CEDA Worker Infected), their bodies gain a new texture effect to make them looked charred.
• In Left 4 Dead, the Common Infected do not have pupils. In Left 4 Dead 2, they seem to have developed reflective eyes, which glow when you shine the flashlight on them, such as in canines or felines.
• One of the symptoms right before turning into a Common Infected is possibly getting cold, as the helicopter pilot states he is getting really cold before the events of Crash Course, in which he turns into a Common Infected.
• The Worker Infected don't seem to have any specific lines when encountered, unlike the other Uncommon Common.
• It is to be noted that the Riot Infected does not count towards getting the "Crass Menagerie" achievement though it is indeed an Uncommon Common. This is due to the ban of abusing government officials in video games in both Germany and Australia.
• The Mudmen are the only Uncommon Common to be unique due to a behavioral adjustment; all other Uncommon Common have unique gear, but otherwise are identical to normal Common Infected.
• It is possible to import Left 4 Dead campaigns into Left 4 Dead 2. However, since the maps don't have any settings for the Uncommon Common, the game will instead spawn them all randomly with the normal Common, including the Fallen Survivor (and possibly the Jimmy Gibbs Infected as well.)
• In the Cut-Version, the Mud Men are not able to obscure the players screen with mud.
• The Jimmy Gibbs Junior infected can apparently be force-spawned by throwing a molotov or Pipe bomb at his stock car. This does not seem to always work effectively, it is possible that it merely increases his chance of spawning. This has only been confirmed for the Xbox 360.
• There is an unused gore effect featuring a gigantic slash completely down the Common Infected's spine. It is possible that this would've been used should the axe had kept its overhead downwards slash and was used on a Common's back.
• The Worker infected are referred to as "Common_male_roadcrew", rather than Demolition teams (Although this is likely due to valve's tendancy towards naming models by appearance, rather than intended name).

[edit] Gallery

Early Common Infected artwork.	A female Infected.	An Infected in a military uniform.	An Infected luggage handler.
An Infected airplane pilot.	An Infected nurse.	An Infected hospital patient.

[edit] References

The Infected
Introduced in Left 4 Dead				Introduced in Left 4 Dead 2			Non-Playable		Cut Infected
The Boomer	The Hunter	The Smoker	The Tank	The Charger	The Jockey	The Spitter	The Witch	Common Infected	The Screamer