Knock, knock. Who's there? Gorilla. Gorilla who? Gorilla cheese sandwich for me, will you, please? Knock, knock. Who's there? Water. Water who? Water you waiting for? Let me in. More than 400 classic knock-knock jokes from the pages of Highlights magazine and other sources will set off laugh attacks every time kids open the book.Knock, knock. Who's there? Gorilla. Gorilla who? Gorilla cheese sandwich for me, will you, please? Knock, knock. Who's there? Water. Water who? Water you waiting for? Let me in. More than 400 classic knock-knock jokes from the pages of Highlights magazine and other sources will set off laugh attacks every time kids open the book.