Slow Left Hand

Also known as the "One-handed Piano Player".

This is what happens when an actor who doesn't know how to play piano is cast as a piano player -- and doesn't get proper instruction on how to fake it. They sit at the keyboard -- sometimes with their hands thoughtfully obscured by the cameraman's choice of angle -- and pretend to play. But while their right hands dance all along the full length of the ivories, their left hands hardly move -- if they move at all, and nothing the cameraman can do short of pointing the camera elsewhere can hide it.

Meanwhile, the music on the soundtrack is obviously played by real pianist who knows how to use both hands.


 * Seen It a Million Times -- I just can't remember where. Lots of 30s musical B-features come to mind, but no specific titles.  Help?