The Spitter

The Spitter is a Special Infected that made her debut in Left 4 Dead 2.

The Spitter's mutations enable her to spit out a ball of mutated stomach acid which, upon hitting the ground, spreads out into a large pool of murky green acid. Any Survivors standing within the pool of acid take increasing amounts of damage based on how long they stand in it, giving the Survivors some time to escape the puddle before taking heavy damage.

When killed, the Spitter leaves a smaller pool of acid around her corpse. She can sometimes be a bit difficult to hear, making somewhat faint squealing noises as opposed to the more distinct noises other Special Infected make, but the hacking noises she makes when she actually spits are easy to hear.

Extent of Mutations
Through mutation of the Infection the Spitter has developed the ability to project an extremely caustic acid from her mouth in a mortar-like fashion, projecting a concentrated ball of damage acid that explodes on contact and spreads into a large pool. This phlegm bomb has the ability to ignite gas cans and propane tanks and will likely be an advantage in Versus games. The Spitter's lower jaw, cheeks, nose and lips seem to be either gone or noticeably eroded, signs that she may not be entirely resistant to the acid she is coughing up. Her proportions are awkward and stretched, including the elongated neck and bloated belly, which are most likely used to accommodate and produce the fluids, and her big toe has shifted to the side of her right foot like the thumb of a hand. While running, a trail of acid can be seen dripping from the creature's mouth. The Spitter's acid might not become acidic until it comes in contact with something in the air. This may be why the acid burns the mouth and nose, but not the stomach.

Survivors

 * If players kill a Spitter with a close combat weapon, they should immediately leave the area before the acid damages them.
 * When the Spitter spits, she'll be slow for a few seconds, then return to normal. Try to use this time to kill her.
 * The Spitter's acid projectile takes a moment to travel to it's target, giving alert Survivors some time to get out of the way. You can also listen for the hacking noise the Spitter makes.

Infected

 * When playing as a Spitter, try to die in front of the Survivor's path. The acid pool created by your death will delay them and give your teammates time to respawn and group.
 * If playing as the Spitter in Versus mode, try to spit on incapacitated survivors so they die quicker.
 * If a Survivor is surrounded by Infected, or even covered in Boomer bile make their day worse by spitting on them. If they are covered in bile they may be so worried about killing all the Infected around them that they will panic and possibly be either too distracted by the spit to kill the Infected, or too distracted by the horde to get out of the spit.
 * The Spitter is one of the most helpful infected. Spitting in survivors who are being choked by a smoker can do extra damage. Also, you can use your acid to separate survivors. For example, if someone is being pounced by a Hunter in a closed area, spit in the survivors path to avoid them saving the helpless one.
 * Your spit causes a lot of panic, because the first thing survivors will try do is get out of it. So having a Charger or a Jockey to catch the survivors while they're trying to save themselves from the acid is a good way to cause damage.

Trivia

 * According to recent gameplay footage, as well as the second Left 4 Dead 2 trailer, the newest Spitter model is permanent. She was made larger, sports a thin, green silk bra and pink thong under her pants, and leaves a green slime trail from her mouth as she walks. Her legs no longer seem lengthened, but her neck is still extended. Her face is mostly deteriorated away, save for her teeth and most interior mouth tissue. When killed, she will rupture, causing the acidic goo to spill and pool where she was killed, along with her body.
 * The Spitter is currently the first female Special Infected to be playable, followed by the female Boomer
 * The Spitter's goo does not seem to harm other Infected, as they are most likely immune to its acidity. This could be very useful for Smokers, Hunters, or even Boomers, as there is nothing much more problematic for a Survivor than to be blinded, standing in acid, being attacked by a horde, and pounced by a Hunter or strangled by a Smoker at the same time. However, she does not seem to have complete immunity, as there are large, irritated burns where her acid seems to have dripped on. Her mouth and face are also extremely twisted and appear to have melted, most likely due to spitting so much acid.
 * The Spitter appears to have an extreme version of the disease known as acid reflux. This is another reference to Special Infected possibly gaining their powers through bodily properties they had before they turned.
 * It should be noted that in Mercy Hospital, one of X-rays shows an elongated neck. It is possible that this X-ray is a person that has been infected with the same strain of the virus as the Spitter.
 * From the Left 4 Dead 2 Demo, Spitter goo apparently has a slight delay from when it hits the ground and when survivors start taking damage from standing in it.
 * In the achievement icon for Great Expectorations, the Spitter seems to look more like a hunched Witch than her current, in game model. This might be down to the fact that in Left 4 Dead 2, there are supposed to be many variants of each Special Infected, implying the one seen here may be another model of the same type of Infected, just like the female Boomer.
 * The achievement Acid Reflex is also an achievement of the game Half-Life 2: Episode 2.
 * When playing as a Spitter, you will slow down for about 2 seconds after shooting goo.
 * The Spitter's attack music cue is called Enzymicide, possibly derived from Enzyme and homicide. This perhaps suggests that not only the gastric acid expelled from the Spitter hurts the Survivors but also the digestive enzymes such as proteases which are corrosive to the protein of human skin.
 * On the Spitter's left hand, one can see 4 wedding rings. This could imply the Spitter was in several relationships previous to the spread of the Infection.