"What's a pirate's favorite letter?"
"I don't know, what?"
"You could guess 'aRRRgh!' Guess aRRRgh."
(several months pass. leaves change, fall, grow back green again. the protagonists age.)
"I've been meaning to ask. Is a pirate's favorite letter 'aRRRgh?'"
"No. It's P, because P is aRRRgh with a leg missing."
"Did you make that up?"
"No. I'm not a genius."