"Left 4 Dead" is a first-person shooter developed and released by Valve. In the game, you fight to escape the small town of Fairfield, which has been recently been overrun by a zombie-like horde. There are a number of cheats that you can type into the game, including one that "lowers gravity," and thus allows both players and zombies to jump higher (this cheat is for the PC version of the game, the Xbox 360 version doesn't have a cheat console).
Begin the game. Select "Options" in the game's main menu.
Select the "Keyboard/Mouse" option in the options menu, then select the "Allow Developers Console" option. Begin playing the game.
Press the "~" option during play, then type the following text into the prompt:
This will enable cheat mode.
Type the following into the prompt:
ent_fire !self addoutput "gravity 0.10
This will lower the game's gravity.