So - I need a puzzle for my campaign I'm running. It needs to go in a door, it needs to be solvable by anyone who is "sane" according to a very alien mentality, and it needs to be insolvable by anyone who is "insane". If it matters, the "insanity" in this case would be roughly described as the mentality of PCs in a game of Paranoia. Oh, and it needs to lock/unlock a door. Any suggestions?
Even if it doesn't work for that, feel free to post other nifty puzzles that you've used or wanted to use in D&D?