It is a moldy, rotten Krabby Patty infested with flies. It contains bacteria-covered buns, rotten meat, melted cheese, a sock, nail pins, a wooden plank, hair, and an eyeball.
Role in episode
Nat Peterson complains to Mr. Plankton about the poor quality of the Krusty Krab's food after Squidward is sent to work behind the grill. Plankton fails to see how the Krabby Patty is any different from the ordinary one until a close-up of it is seen, after which he calls Squidward to have a talk about his bad cooking.