Charlie Chaplin "A Dog's Life"

Alright, so I was watching a charlie chaplin movie called "A Dog's Life", and at the part where it says "a new singer sings an old song" a woman who looks alot like Clara Rockmore goes onstage. Right when I was thinking that it might be her, to imitate the sound of singing, a theremin starts playing as she pretends to sing. Aparently it isn't clara rockmore, but it looks like her, and it would be around the same time. and its kind of a coincidence that they use the theremin.
here are the pictures, first of Clara (http://www.perfectpitchpeople.com/rockmore%20image.jpg), and then of the chaplin woman (http://chaplin.bfi.org.uk/images/420/dogs-life.jpg). similar, no?

okay I'm done.

Check out http://www.imdb.com/title/tt0009018/fullcredits#cast

yeah, "Edna Purviance." Still, they did use a theremin as the "singing."