The Spitter

The Spitter is a new Special Infected to appear in Left 4 Dead 2.

It makes a hacking sound before spitting out what appears to be a ball of mutated stomach acid, which upon hitting the ground spreads out similar to a Mortar round and changes from a sickish green gas-like substance to blood red. Any survivors within the area receive massive quantities of damage over time. This makes it exceedingly difficult to camp in one place for too long, otherwise the Survivors' health will quickly whittle away. In a sense, the Spitter could technically be considered an Infected with molotovs. It can be assumed the substance it shoots from its mouth has corrosive properties, although it appears unable to pass through obstructions, even bouncing off hard surfaces such as walls. This brings to mind the question of whether or not the Infected could effectively spit at a wall from an angle and divert its acid to a camping group around the corner.

The Spitter was designed to split up tightly packed groups of survivors to make them easier to pick off by the other Special Infected, just like the Charger's primary objective.

Extent of Mutations
The Spitter's lower jaw, cheeks and lips seem to base either gone or noticeably eroded. This is most likely due to a mutation caused by the infection, or damage from the acid it coughs up. The creature's body proportions are awkwardly stretched, including the elongated neck, and the belly seems slightly bloated, most likely to accommodate and produce the fluids.

It appears to be mutating in the same fashion as the Boomer, with its gut expanded, (probably still growing). It seems likely that, unlike the Boomer's bile, its spit can only cause damage, not attract the Horde.

The Spitter's limbs are also noticeably elongated. There is no known reason for this as of yet, other than to make the Spitter more frightening in appearance.

Trivia

 * According to GameSpy, its graphics and design are still being worked on.
 * In one of the new comic con videos, the Survivors see a dead Spitter briefly on the wooden bridge. This Spitter lacks the high heels, and doesn't have quite as long a neck.
 * So far, The Spitter seems to be the only Infected (Common or Special) to possess pupils, however, since its design is still being worked on, it is unknown if they will be kept in the final product.
 * The concept of the Spitter is very similar to a zombie of the same name from Jenny Romanchuk's The Zombie Hunters comic. However, there is no evidence that the game developers were aware of this webcomic.
 * The Spitter may be what happens when the virus that effects a Boomer effects a female. Both seem to have big stomachs, and both spit out some type of vomit. It could be that the Boomer virus has become even stronger, resulting in the Spitter's damage-causing attack.