The girl, who was reading a book, 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," she 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 girl replied, "Do you really feel qualified to discuss nuclear power when you don't know s**t?"