Rules of exodus

Exodus is a game which involves running out or away from somewhere as fast as possible. Such as a school or work place. Basically somebody shouts out "EXODUS" or "PURGE" and when either of these are shouted everybody who plays the game must run out or away from wherever they are. The game can be played at any time any place and is extremely funny when you run past people who are not playing as they wonder why you are running and shouting!!