Here's a riddle I've stolen from a Buddhist forum. See what you guys make of it, I havn't quite gotten my mind around it yet! The answer to both questions is one. If you find the answer, you win the prize. Once you see the prize, you know the questions. If you keep the prize, your answer is wrong. What is the answer?
OK, here's a theory. The answer to both questions is one. Ie the same. One of the questions is what is the answer, clearly. If you see the prize you know both the questions, so I think the other question is what is the prize? So the answer and the prize are the same thing (usually the case with riddles, since the best thing you can get out of a riddle is finding out the answer). I think the answer is a secret. You win knowledge of the secret if you find the answer. If you keep the secret then you're telling people that the answer is something else so in effect you're giving the wrong answer.