Like many others, I assumed that Mickey's wild dancing in this cartoon was done by Ward Kimball. Kimball used it under the end credits of The Mouse Factory, a TV series that he produced for Disney. However, we can see that the animation was done by Ken Muse and Riley Thomson.
Muse is better known for his work on the Tom and Jerry series, but he made an impression on somebody at Disney who talked to film critic Frank Nugent. In 1947, Nugent wrote an article called "That Million-Dollar Mouse" for the N.Y. Times Magazine. It's reprinted in the book Walt Disney Conversations edited by Kathy Merlock Jackson. In the article, Nugent writes, "Artists like Fred Moore, Marvin Woodward, Les Clark and Kenny Muse have helped [Mickey] to express himself." This was half a dozen years after Muse left, but his name still came up in connection with the Mouse.
Muse only gets three scenes here, but the third one is just plain stunning. Muse was a very strong draftsman and as wild as Mickey's action is, the drawing stays controlled. Mickey is appealing in every drawing.
Thanks to Galen Fott, you can click here and see a rough drawing of Mickey dancing by Ken Muse. Note the difference in costume. That led to some confusion as to whether the drawing came from Mickey's Surprise Party (a 1939 World's Fair industrial Disney did for Nabisco) or Mickey's Birthday Party. We've determined that the drawing doesn't appear in the industrial, so my guess is that Muse animated the scene before somebody decided to change Mickey's outfit. Some poor assistant animator got stuck making the change.
Director Riley Thomson follows Muse to wrap up Mickey's dance and in my opinion is even better. Thomson is more willing to push his timing accents, uses a stronger line of action and is generally more willing to distort Mickey for effect. I can imagine Thomson directing this cartoon and deciding the scene was too juicy to give away, so he kept it for himself.
This cartoon is heavily cast by character, and Bernie Wolf gets Donald. Wolf was an important animator in the '30's, working for Fleischer, Iwerks and Disney. He was in the First Motion Picture Unit during the war and later worked for Hanna Barbera and Film Roman, though I have no idea what he was doing in the period between the war and his TV years.
Scene 28 starts out with some solo dancing by Donald, and Wolf is willing to push his poses for the musical beats as much as Les Clark. What's really interesting is that for scenes 36.2 and 36.4, Clark and Wolf each take a character in the scene. 36.4, in particular, has a lot of character interaction. Donald rides on Clara's rear and she bounces him against the wall several times. I'm guessing that Clark had to go first, with Wolf working to Clark's drawings. When the interaction really gets wild in scenes 40 and 40.1, it was impractical for two animators to handle it, so Clark did it all.
This is the third Mickey cartoon directed by Thomson that's been discussed here. They're great cartoons and every one of them contains great animation. It's clear that Thomson valued that, being an animator himself, and he really gave his crew opportunities to shine.