It's always a treat to hear a theremin in a movie score. It's even more rare to see one.
Jerry Lewis' comic dance with Samuel Hoffman's theremin in The Delicate Delinquent is the most famous appearance of a theremin on screen.
There is a theremin player in an Argentinian film, The Holy Girl, and it is featured in the recent Spanish short Martians Go Home!.
Though not a complete theremin, The Thin Man's opening scene (pictured up top) shows a scientist moving a box of tubes to and fro in front of a generator making its humming pitch change. The scene sure echos the moment the theremin was invented, and the actor even looks like Leon Theremin!
(Edward Ellis)
It would be great to start building a list of films were the theremin makes an on screen appearance. Do you know of any more?