The Worm Turns 1937

Directed by Ben Sharpsteen

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.