A stranger was  seated next to Little Johnny on the plane when the the
stranger turned to  the Little Johnny and said, "Let's talk. I've heard
that flights will go quicker if you strike up a conversation with your
fellow passenger."
Little Johnny, who had just opened his book, closed it slowly, and said
to the stranger "What would you like to  discuss?"
"Oh, I don't know," said the stranger. "How about nuclear power?"
"OK," said Little Johnny. "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?"
"Jeez," said the stranger. "I have no idea."
"Well, then," said Little Johnny, "How is it that you feel qualified to
discuss nuclear power when you don't know sh*t?"