do you know sh*t?

A guy was seated next to a 12-year-old boy on a train. Being bored, he turned to the boy and said, "Let's talk. I've heard that train rides go quicker if you strike up a conversation with others."

The boy, who was reading a comic, closed it slowly and said to the guy, "What would you like to talk about?"

Oh, I don't know," said the guy. "How about nuclear power?"

"OK," he said. "That could be an interesting topic. But let me ask you a question first. A horse, a cow and a deer all eat the same stuff... grass. 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?"

The guy thought about it and said, "Hmmm, I have no idea."

To which the boy replied, "Do you really feel qualified to discuss nuclear power when you don't know sh*t?"