Two strangers were seated next to each other on the plane when  the first guy turned to the second and said, "Let's talk.  I've heard that flights will go quicker if you strike up a conversation with your  fellow passenger."
 
The second guy, who had just opened his book, closed it slowly,  took off his glasses and said to the first guy, "What would you like  to discuss?"
 
"Oh, I don't know," said the first guy.  "How about nuclear power?"

 "OK," said the second guy.  "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 first guy.  "I have no idea."
 
"Well then," said the second guy, "How is it that you feel qualified to discuss nuclear power when you don't know shit?"