The Worm Turns
Mad scientist Mickey has just brewed up a potion; to test it out, he squirts it on a fly that's been trapped by a spider, a (regular) mouse being harassed by a cat, then the cat when Pluto goes after it, and Pluto when dogcatcher Pegleg Pete goes after him. Each of the underdogs turns against his tormentor.
Genres: Animation
Directors: Ben Sharpsteen
Writers: Otto Englander
IMDB: tt0029797