Easter egg

An Easter Egg is a small secret in games. Easter eggs usually doesn't associate itself with gameplay, but players usually find easter eggs due to interest in them. Easter eggs are secret stuff that was left in the game. An example is the cheese that secretly appears in every level of the game Perfect Dark.

Examples of Easter Eggs in Mario games:
 * In Super Mario Galaxy, in the Toy Time Galaxy, a secret train set appears.
 * In Donkey Kong 64, a picture of a strange frog appears.