The Marshmallow Test - Kids are left in a room alone with a marshmallow, saying that if they wait long enough, they’ll get ANOTHER when the surveillor comes back. Hilarity ensues.
There’s apparently nothing like watching a kid squirm over a marshmallow. My favorite is the red-headed girl, who just eats the marshmallow as the proctor is walking out the door. After she’s done, she takes her plate, gets up, and walks to the door.