Flat tyre

In my youth I had a small Austin car. One day I got a puncture and pulled up, right outside a lunatic asylum. As I went to swap the flat for the spare I accidentally knocked the four wheel nuts down a storm-water grating, far out of reach. As I berated my clumsy self and wondered aloud how the hell I was going to get out of this predicament an inmate popped his head over the fence to see what all the fuss was about. He said "Just remove one nut off each of the other three wheels and use them to mount your spare, then drive slowly into town, find an automotive parts supplier and buy four replacement nuts". I said "wow, thanks very much for the good advice, tell me, how come someone as sensible as you is in the loony-bin?" He said "I'm mad, not stupid!".

Cheers,
Geoff.