In comedy it's the subtle art of starting a joke going in one direction, or even making a complete joke, but then going in a completely different direction with the punchline or second joke. For example, in an Mr. Bean skit he goes through all this crazy stuff to pack his junk into a tiny suitcase and finally manages to do it. Then he sees he's forgotten like a sock or something. So he pulls out a bigger suitcase and puts the smaller suitcase in the bigger one with the sock. Wait, that's not right.