Infected: Boomer

BOOMER: a bloated infected whose vomit and bile (which may be released at will and upon death) blinds the player briefly and attracts a horde of common infected. He is recognized by a very faint and putrid moaning sound. This sound is intensified when in closed off buildings, such as in a kitchen or hallway. -from Wikipedia.

BOOMER: an extremely bloated Special Infected. Its mutation has caused it to produce vast quantities of bile, which it uses as a projectile attack by vomiting. If it hits the Survivors, the bile covers them, temporarily blinding them and attracting the Horde. A powerful but fragile Infected, the Boomer's role in Left 4 Dead and Left 4 Dead 2 is to slow down and sow confusion amongst the Survivors as a group, giving the rest of the Special Infected an opening to eliminate each individually. -from The Left 4 Dead Wiki.

BOOMER: Huge and obese infected that vomits like a fire hose. Can be shot while strafing. When it hits a survivor with its vomit, the vomit acts as a pheromone to the AI controlled normal infected and causes them to focus their attack on that player. The Boomer gets points for all attacks against the target by infected. Moves slowly. Also, when killed, the Boomer does as his name says and explodes, causing all nearby Survivors to become puked on. -from Left 4 Dead 411.

A boomer from "Left 4 Dead".