An American Man and a Little Iranian Girl

An American man was seated next to a little Iranian girl on the airplane, when the stranger turned to her and said, 'Let's talk. I've heard that flights go quicker if you strike up a conversation with your fellow passenger'. The little girl, who had just opened her coloring book, closed it slowly and said to the stranger: 'What would you like to talk about?'
'Oh, I don't know,' said the American. 'Since you are Iranian, how about nuclear power?' 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 American, 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 power... when you don't know shit?'