Easter egg

Easter Eggs are intentionally hidden messages or features included in a movie, video game or DVD. Easter eggs in DVDs can often be found by an extra click to the right or left or going up in the menu instead of going down to select a choice, which will bring up a hidden feature.

Easter Eggs in Futurama DVDs
DVD Releases with Easter Eggs.
 * Volume Three-Disc one.
 * Monster Robot Maniac Fun Collection-Al Gore Easter Egg.
 * The Beast with a Billion Backs-Old Farmer's Wikipedia Easter Egg.