A stranger was seated next to Little Tommy on the plane when the stranger
turned to the boy and said,
"Let's talk. I've heard that flights will go quicker if you strike up a
conversation with your fellow passenger."

Little Tommy, who had just opened his book, closed it slowly, and said to
the stranger, "What would you like to discuss?"
"Oh, I don't know," said the stranger. "How about nuclear power?"
"OK," said Little Tommy. "That could be an interesting topic. But let me ask
you a question first - A horse, a cow, and a deer all eat grass. The same
stuff. Yet a deer excretes little pellets, while a cow turns out a flat
patty, and a horse produces clumps of dried grass. Why do you suppose that
is?"
"Jeez," said the stranger. "I have no idea."
"Well, then," said Little Tommy, "How is it that you feel qualified to
discuss nuclear power when you don't know shit?"