DM: Put the first piece of key in, and then try those four ends.

You put in the first piece of the key, and surprisingly, it goes right in! Now just to figure out which other half is the right one... if any. You hope it's one of them, otherwise you definitely just broke the door. You're sure you could draw this out for a few pages in a classic bit that is surely just as funny as you think it is, but instead you just quickly try each key.