Cow Goes Moo

Alright, listen up, buttercup. This here's a knock-knock joke, see? It's all about playin' with words. The punchline is that “Cows don't go who, they go moo” sounds like “Cows don't go 'who', they go 'moo'” which is what cows actually say. If you have ever been to a farm (probably not), you would know that cows say "moo." It is a play on words you couldn't comprehend because you have rocks for brains.