Knock knock. Who's there? Cows go. Cows go who? Cows go moo not who.
Knock knock. Who's th.... Interupting pidgeon.
Knock knock. Who's there? Isabelle. Isabelle who? Is a bell necessary on a bicycle.
Knock knock. Who's there? The Police. The Police who? You're parents were killed in a car accident.
Knock knock. Who's there? Atch. Atch who? Sorry I didn't know you had a cold.
Knock knock. Who's there? Boo. Boo who? No need to get upset, it's only a joke.
Knock knock. Who's there? Match. Match who? Oh, hi Matthew, come in.