Interrupting Cow

Alright, listen up, buttercup. This is a knock-knock joke. Someone says "Knock knock," and you ask, "Who's there?" Then they give you a name, like "Interrupting cow." So you're supposed to say, "Interrupting cow who?" But the joke is the cow interrupts you by saying "MOO!" before you can finish the "who" part. Get it? You wouldn't, otherwise you wouldn't be reading my explanation! Haha! I am so smart. S-M-R-T!