Unlocked

JohnB: Elaine, what key is the hardest to turn?

Elaine: Hmm, well let’s think about that. No, I’ve no idea. What’s the answer John?

JohnB: A donkey!

^{Source: “A Thousand and One Riddles, With a Few Thrown In”, Publisher George Routledge and Sons Limited, London (A Victorian book of riddles).}