For the past several years, John has been working at the city zoo. He enjoys his job a lot... except for one part. Every day, he has to give a keeper talk at the polar bear exhibit, and he hates public speaking. To make it worse, it's a very popular talk, so there are always lots of people there, and it usually takes half an hour to get through all of it.
On one particularly busy day, John is grousing about it to his friend Bill, who mans the zoo's ice cream stand, right across from the polar bears, when Bill hits on a genius idea. "Why don't I do it for you? I've heard you give that same speech hundreds of times, I'm sure I know it as well as you do. It'll give you a break and give me something else to do."
John loves the idea, so he pulls of his keeper work shirt and hands it to Bill, who gives him his staff shirt in return and asks him to man his ice cream stand while he does the talk.
As John watches from the ice cream stand, Bill ends up giving a wonderful keeper talk. He remembers every fact, every joke, and the audience is loving it. Everything is going perfectly until the very end, when he solicits questions. All of them he fields easily, having heard them so many times before - what are their names, what do they eat, how old are they - and then a young woman raises her hand.
"Yes, excuse me? I'm actually a grad student over at the university, and I'm doing my thesis on polar bear thermoregulation. Could you please tell me how the insulative properties of polar bear fat evolved, and what the projected timeline would be for its de-evolution in the face of global climate change?"
Bill stares blankly for a moment, and then smiles. "Young lady," he says, "that's an incredibly easy question. In fact, it's so easy," beckoning John over, "that I bet even our ice cream man can tell you the answer."