The hard, spongy textured layer of jello found at the bottom of the bowl. It formed when jello isn't eaten for a number of days, thus becoming hard and losing taste. The act of biting into this layer gives you a nasty taste and texture in your mouth...SURPRISE!
Mom: Tonight we're going to your aunt's house to have dinner.
Child: Oh great...then for dessert we get to eat Uncle Don's week old jello with the jello surprise.