– Where can I lock up my clock while I’m away?
– Why not lock it in your locker?
– I’m afraid my locker won’t lock.
– Oh.
– Can I lock it in your locker?
– No, I’m afraid you can’t.
– But surely you’ve got room for a small clock.
– Yes, plenty. But my locker won’t unlock.
– I see.
– That’s why I’ve been borrowing your clock.