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 into a large pool of murky green acid. 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 be depleted. 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. She apparently also possess the ability to jump high distances, as seen in one of GameTrailers videos. In that video, she is seen jumping to the height of a roof, spitting the acid at the Survivors, and then falling down, however, it is unknown if she still possesses this ability since the Spitter got a model change and was made fatter.

The Spitter was designed to prevent Survivors from sitting still in corners and to make them easier to pick off by the other Special Infected, similar to the Charger's primary objective.

Extent of Mutations
The Spitter is the second female Special Infected to appear within the Left 4 Dead franchise. Through mutation of the infection, it has developed the ability to project an extremely caustic acidic phlegm from its mouth, in a mortar-like fashion in that it is projected in a concentrated ball and on contact it spreads into a huge puddle of acid. The Spitter's lower jaw, cheeks and lips seem to be either gone or noticeably eroded. This shows that it may not be entirely resistant to the acid it coughs up. The creature's body proportions are awkwardly stretched, including the elongated neck, and the belly seems bloated, most likely to accommodate and produce the fluids. It also appears that the creature's stomach glows an eerie green, showing that this is where the acid is perhaps stored. Whilst running, a trail of acid can be dripping from the creature's mouth.

Trivia

 * According to GameSpy, its graphics and design are still being worked on. Presumably as some find the Spitter disturbing, and others find it extremely goofy looking.
 * 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.
 * According to recent gameplay videos from the PAX, the Spitter's goo no longer turns red but retains a bright green color constantly. It is also noted that the Spitter's stomach appears to glow with the green goo.
 * In one of the video from GameTrailers, you can see how the Spitter's model was changed. She was made fatter and leaves a green slime trail from her mouth as she walks, she also has normal legs but her neck still seems to be extended, she also appears to have lost her teeth, and when killed, she will "melt" and leave a small pond of the acid she spits (The body, however, does not actually disappear).
 * In the previously released artwork, The Spitter possesses pupils, but since her image has changed, it is unknown if they have been kept.
 * The Spitter is currently the first and only playable female Special Infected.
 * The Spitter's ability is possibly a way to stop the survivors from cornering.