Anchors Aweigh question

I tuned in to Anchors Aweigh on TCM yesterday just in time for the animated sequence: Gene Kelly talks to a bunch of animals in the forest about how their king has banned music and dancing, and then visits the king, played by Jerry the mouse. Kelly then teaches Jerry how to dance. It is, of course, a famous scene. I saw in one of the documentaries on Kelly (I think) that aired on TCM that Kelly wanted to use Mickey Mouse in the dance, but that Walt Disney was unsurprisingly opposed. Disney afterwards was apparently quite impressed by what Kelly had done. But I would have thought that the suits at MGM wouldn't have liked using Mickey Mouse when they had their own cartoon mouse, as opposed to Hollywood Party back in 1934.

Anyhow, there was one thing that struck me about the dance scene: Jerry tapped! I don't mean that he was doing the same sorts of steps that Gene Kelly was; that's to be expected. But I could swear that I heard Jerry's steps making tapping sounds! It's not as if Jerry had any tapping shoes on; in fact he was naked as the day God made him, as opposed to Mickey, who at least has the decency to wear short pants. So where was the sound coming from? Well, presumably Jerry added the taps in post-production. :-) But don't they have a continuity editor for this stuff?