Knock Knock Joke 
Knock, Knock.
Who's there?
Interrupting Cow.
Interrupting C...
MOO!
Knock, Knock.
Who's there?
Cows go.
Cows go who?
No, silly, Cows go MOOO!
Knock Knock
Who's There?
Pizza
Pizza Who?
Pizza on Earth, Good Will to Men.
Knock, Knock
Who's There?
Murray
Murray Who?
Murray Christmas to all, and to all a good night.