SpongeBob SquarePants - Image #662,110

"Chum" is dead fish.
The Chum Bucket restaurant is made of some kind of metal.

What bothered me more about this was the episode about how Mr. Crabs discovered the Crabby Patty formula. It is revealed that the formula Plankton uses for Chum is almost the same as the Crabby Patty, but it is missing a few secrete ingredients or spices, otherwise, they are the same thing. This is why he is so eager to steal the formula or experiment with new ingredients, because he is almost there.

So yeah… Crabby Patties are also chum, they just taste better.