Audio Cues

Certain events in Left 4 Dead and Left 4 Dead 2 have associated audio cues. These can range from hearing a tank before it spawns to tracking down a hunter.

Special Infected
Note: For those who are not quite as musical, each special infected has a different number of notes in their audio cue.

2 notes: Smoker

3 notes: Hunter

4 notes: Spitter

5 notes: Boomer

6 notes: Charger

8 notes: Jockey

Boss Infected
These infected do not have preset audio cues by the game, but they do have boss music and do make their own idle sounds.