Want to hear a joke? Knock Knock.
Want to hear a joke? Knock Knock.
user
Knock Knock. 
Who's there? 
Boo. 
Boo who? 
Don't cry, it's just a joke!
assistant
Want to hear a joke? Knock Knock.
user
Who's there? 
Boo.
Sorry, we don't accept spoooky business here!
assistant