The keys of the piano are manipulated by short pieces of rubber hose (fingers) that I made from automobile vacuum line. The fingers are friction mounted in holes on a laminated plywood wheel that I rotate with a hand crank. I made the ratcheting mechanism from a toggle bolt - this keeps you from turning the crank in the wrong direction.
The wooden mouse is attached to the flat rubber belt with an old fashion thumb tack. I got the belt from an old computer or printer.
It was only when I was preparing this instructable that I realized I didn't put a tail on the mouse!
Happy Birthday Alexandra!