Brains.

Remember on Sesame Street, when beloved corner shop owner Mr. Hooper died? And then the adults in the neighborhood had to explain to Big Bird that Mr. Hooper wasn't going to be coming back? I think that was one of the most touching and powerful moments in not just children's TV, but in all television history.

When Mr. Hooper's zombified corpse returned and devoured the original Gordon? Slightly less touching. But about 100 times as awesome.