A professor finds himself sitting next to a farmer on a train. Bored, the professor decides to propose a game to pass the time.

“I’ll ask you a question,” the professor says. “If you can’t answer, you give me $5. Then, you ask me a question. If I can’t answer, I’ll give you $500. What do you say?”

The farmer nods in agreement.

The professor starts, “What is the distance between the Earth and the Moon?”

The farmer silently pulls out $5 and hands it to the professor.

Now it’s the farmer’s turn. He asks, “What animal has three legs when climbing a mountain and four legs when coming down?”

The professor is stumped. He racks his brain, searches for logical explanations, and even consults his notebook, but he can’t find an answer. Frustrated, he hands over $500 to the farmer.

The farmer takes the money with a smile and leans back to take a nap.

Curious and unwilling to let it go, the professor shakes the farmer awake and asks, “Alright, what animal is it?”

The farmer silently pulls out $5, hands it to the professor, and goes back to sleep.