The bits of animals that they couldn't sell as real meat, which subsequently end up in other products which claim to contain meat (although no one can actually tell you what kind of meat they're supposed to be), e.g. doner kebabs, hot dogs, McNuggets, etc.
Dude 1 - "I don't believe you're eating that Doner. You know what those things are made of?"
Dude 2 - "Nope."
Dude 1 - "Lips and arseholes!"