Siu's mind fart thread reminded me of my favorite puzzle question.
You go on a game show where you have three doors in front of you, and you simply have to pick a door to win a prize. Behind one of the doors is a pot of gold, behind the other two doors are bad prizes, say a couple of jsharr's delicious basses that passed their sell-by date.
You pick Door #1, and the host says "Before we open Door #1, we're going to give you a choice. First, let's open up a door that you did not choose." So they open up Door #3, knowing that a bad prize is definitely behind it (i.e., they will always open a door with a bad prize behind it).
The host says "OK, now you know that the pot of gold is behind Door #1 or Door #2. You can stick with your original choice of Door #1, or you can now switch your choice to Door #2. What do you want to do?"
A. Stick with Door #1.
B. It doesn't matter, the odd are 50-50 between Door #1 and Door #2.
C. Switch to Door #2.