We have a music box. My parents bought it from a tourist shop and gave it to the kids. You turn a crank, and it plays "O Canada".
It's a classically designed music box too, if inexpensive. The crank turns a wheel with raised points that lift up and release tuned prongs to play the right notes.
Fiddling around with this music box, I was disappointed to see that it only turned in one direction. "Darn," I thought. "I wanted to know what O Canada sounded like, backwards."
As Erin was there, I looked up at her. "What do you think O Canada sounds like if played backwards."
She thought for a moment, then looked at me. "Oh, say, can you see."
Which was exactly what I was thinking!