A stranger next to a little girl on the plane?

A stranger seated next to a little girl on the airplane

turned to her, "Let's talk. Flights go quicker when you strike up a conversation with your fellow passenger."

The little girl, who had just opened her book, closed it slowly and said to the stranger, "What would you like to talk about?"

"Oh, I don't know" said the stranger. "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 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?"

The stranger thinks about it and says, "Hmmm, I have no idea."

She said "Do you feel qualified to discuss nuclear power when you don't know ****?"