The Man In The Seat Next To Him Was Bothering Him. What He Said Next? Ouch

A stranger was seated next to Archie on the plane when he turned to him and said, "Let's talk. I'm Wallace. I've heard that flights will go quicker if you strike up a conversation with your fellow passenger." 

Archie, who had just opened his book, closed it slowly, and said to the man, "What would you like to discuss?" 

"Oh, I don't know," said Wallace. "How about nuclear power?" 

"OK," said Archie. "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 Wallace. "I have no idea."

"Well, then," said Archie, "How is it that you feel qualified to discuss nuclear power when you don't know sh–t?"