Knock Knock

Sammy's current favorite joke:
Knock Knock
Who's There?
House.
House who?
House it goin'?

Katie's current favorite joke:
Knock Knock
Who's There?
Boo
Boo who?
Don' cry. 'S'only a knock knock joke!

My current favorite joke that I learned from Sammy:
Knock Knock
Who's There?
Chooch.
Chooch who?
Choo choo? Are you a train?