"What are you smiling about?"
"You can't just smile about nothing."
"Well, I am!"
"Come now, that doesn't make sense."
"Oh, I don't know. It feels awfully good. What are YOU so serious about? Has the roof caved in?"
"No, I don't think I'm serious about anything in particular."
"Well, does that make sense? You say I may not smile at nothing, and yet you can be serious about nothing at all."
"That really doesn't make sense, does it? I think you've got the best of the deal at that."