Bugs

Glitches are an unwanted result of coding or programming of a game. There are many glitches in Left 4 Dead that can be used for achievements, an advantage in versus, or just for fun. Glitches can be preformed on any system without the use of a command prompt on the PC. Glitches are normally patched out by a download that fixes them, so normally very well known glitches won't exist for long.