"Knock Knock - Seymour" joke

Knock Knock
Who's there!
Seymour!
Seymour who?
Seymour if you look out of the window! Knock Knock
Who's there!
Seymour!
Seymour who?
Seymour if you have a pane of glass in your door! Knock Knock
Who's there!
Seymour!
Seymour who?
Seymour if you open the door!