A man gets on a plane and is seated next to a young kid. The kid won't stop talking during the flight so the man turns to him and says, "Lets talk."
The kid replies, "Okay, what do you want to talk about?"
The man replies, "How about string theory?"
The boy says, "That's a very interesting topic. But first, do you know why rabbits, horses, and cows poop all have different poop even though they all eat grass?"
The man replies, "I have no idea."
The boy smiles and says, "How do you expect to discuss string theory when you don't know shit."