The Worm Turns is a 1937 Mickey Mouse cartoon, directed by Ben Sharpsteen.
Mickey finds a formula for a "Courage Builder" in an old book. He whips some up and discovers it has the power to turn the food chain upside-down, allowing prey to turn on and overcome their predators, as seen when he tests it on various animals.
- All Webbed Up: Mickey's first test subject for the Courage Builder is a fly trapped in a spider's web. The fly manages to not only escape, but pummel the spider and trap him in his own web.
- Butt Biter: Pluto does this to Pete when he takes the formula.
- Cartoon Bug-Sprayer: What Mickey uses to dispense the formula on Pluto.
- Cats Have Nine Lives: When Pluto corners the cat and closes in for the kill, the cat's nine lives emerge from its body, in the form of cat ghosts, each adorned with the numbers 1 through 9 on it. Mickey sprays the formula on the cat just as the last life is coming out, and all the other eight jump back in as the cat gets a boost of courage and goes on the offensive against Pluto.
- Diabolical Dogcatcher: Pete takes the role of a cackling, evil dogcatcher roaming around to kidnap people's pets, stuff them in his wagon and take them to the pound. When Pluto tries to escape, he even pulls out a shotgun while chasing him, intending to flat-out murder the dog while yelling death threats at him.
- The Dog Bites Back: Happens when any and all prey takes the Courage Builder. Pluto is a literal example when he takes it.
- Dogs Love Fire Hydrants: After Pluto defeats Pete, he stops to sniff at a fire hydrant. Mickey sprays Courage Builder on the hydrant, and it attacks Pluto with a Hydrant Geyser.
- Furry Confusion: Mickey has a real mouse in his house, which he uses his Courage Builder on when it's threatened by a cat.
- Human Hammer-Throw: The mouse dispatches the cat by grabbing him by the tail, swinging him around, and throwing him out the window.
- The Hunter Becomes the Hunted: The Courage Builder allows any creature it's used on to become brave and fearsome, allowing flies to turn on spiders, mice to beat up cats, cats to terrorize dogs, and dogs to viciously attack dogcatchers.
- I'll Kill You!: As Pluto resists Pete's attempts to capture him, the latter flat-out yells death threats at the dog as he pursues him with a shotgun, saying things like "I'm gonna fill ya full of lead!" and "I'm gonna blow your head off!"
- Mad Scientist: Mickey plays at one, recreating a potion found in a book of "Ancient Formulae".
- Make Me Wanna Shout: After getting sprayed by the Courage Builder, the cat screams at Pluto loud enough to blow him away.
- Oh, Crap!: The predators' typical reaction to the prey turning on them, thanks to the Courage Builder.
- Primal Chest-Pound: The first thing the mouse does under the effect of the Courage Builder is pounding his chest and letting out a Mighty Roar.
- Shake Someone, Objects Fall: When Pluto bites Pete on the rump and shakes him, various things fall out of Pete's pockets, including a blackjack, a steak, a handkerchief, a coin purse, and a pocket watch.
- Villainous Breakdown: When Pluto resists Pete trying to capture, Pete winds up accidentally opening the door of his dog catcher's truck and releasing all the dogs imprisoned in it, after which Pete resorts to taking a shotgun and simply trying to shoot Pluto with it!
- Villainy-Free Villain: Pete isn't technically doing anything illegal — he has a job to do and is charged with keeping dogs off the streets — but does get too gleeful and violent while doing it.