Nuclear Deal

A stranger was seated next to a little girl on the airplane when the stranger turned to her and said, 'Let's talk. I've heard that flightsgo quicker if 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 deal?' and he smiles.
'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 stranger, visibly surprised by the little girl's intelligence, thinks about it and says,
'Hmmm, I have no idea.' To which the little girl replies,'Do you really feel qualified to discuss nuclear deal when you don't know shit?