it looks big and tough but it is only big

A stranger was seated next to Little Johnny on the
plane when 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 shit?"