After getting ejected from a horse-drawn carriage during a stormy night, Tom seeks shelter in the castle of a mad scientist, where he encounters not just his lifelong nemesis Jerry, but also a cat whose brain has been switched with that of a dog. Tom's attempts to catch Jerry from this point are thwarted by the dog-brained cat, who is hellbent on defending his little rodent compadre.
Tropes:
- Animal Testing: A less painful example compared to this trope's usual fare. The mad scientist frequently switches the minds of the animals that he has rounded up in his laboratory through the use of a body-swapping device.
- Big Friendly Dog: Well, Big Friendly Dog-Brained Cat, anyway. The orange cat isn't that huge in comparison to the human mad scientist, but he is viewed as such to the smaller Jerry.
- Breaking the Fourth Wall: The cartoon ends with Jerry winking at the audience after a frightened Tom flees the castle, never to be seen again.
- Brick Joke: The beginning of the short has a dog getting his brain switched with the orange cat. Later, as Tom is trying to escape from the castle, he opens a door revealing said dog, who meows at him.
- Buried Alive: After clobbering Tom on the head with his bone, the dog-brained cat then takes him outside and buries him in the ground before running back inside the castle. The rain then causes Tom to grow from the ground like a flower.
- Cats Are Mean: Tom, compared to the rest of the Gene Deitch shorts where he is portrayed as a pitiful Butt-Monkey just trying to do his job as a mouse catcher. Later, he finds a "Lovable Cats" book in the castle's library where all of the cats mentioned in it avert the trope. Not that it convinces the dog-brained cat in the least.
- Exactly What It Says on the Tin: The cat who serves as a foe to Tom in this cartoon has his brain replaced with that of a dog.
- "Freaky Friday" Flip: The orange cat and the blue bulldog at the beginning get their bodies switched around by the mad scientist, resulting in the former barking angrily at the scared latter.
- Haunted Castle: The main setting of the cartoon, where Tom goes to after his ejection from the carriage.
- The Hyena: Staying true to the "mad" part of his title, the mad scientist constantly laughs like a hyena overdosed on crack.
- Laughing Mad: The mad scientist, naturally.
- Logo Joke: Jerry reclines inside his mouse hole as he roars like the MGM lion, with the hole even bearing the filmstrip ribbon around it to complete the effect.
- Mad Scientist: Naturally, the castle is home to a deranged, cackling mad scientist whose favorite pastime is switching the brains of animals, with Jerry serving as his assistant.
- Match Cut: The close-up of the cat seen in the "Lovable Cats" book fades to a shot of the dog-brained cat doing the same pose as the cat in the picture.
- Mouse Hole: The mouse hole seen in this cartoon is special from the other ones in the franchise in that it is adorned with the MGM ribbon, which Jerry uses to reenact the MGM logo and scare the crap out of Tom.
- Non-Standard Character Design: The mad scientist is drawn in a very stylized design that wouldn't be out of place in a UPA cartoon, making him stick out like a sore thumb from the rest of the characters in the cartoon. Then again, this is Gene Deitch we're talking about.
- Palette Swap: The dog-brained cat is little more than just an orange-colored Tom.
- Prehensile Tail: After coming back into the castle to see Jerry and the orange cat sleeping together, Tom tries to slice Jerry in half by taking a blade from one of a pair of axes on the wall, sliding it through the cat's tail, placing Jerry underneath the tail and letting go of the cat's tail so that it will come down on Jerry. Unfortunately for Tom, the dog-brained cat wakes up before Tom does so and stops his tail from hitting Jerry. After grabbing Jerry close to him, the cat then swings his axe-tail down on Tom and hits him right into a set of beaker tubes where he gets sucked through them.
- Screw This, I'm Outta Here: After his final attempt to catch Jerry fails, Tom is left running for his life from the castle. He opens doors that lead to a tweeting elephant, a bleating chicken and the cat-brained dog from earlier, and after encountering a mooing cuckoo clock, Tom encounters Jerry and begs him to squeak like a normal mouse. Unfortunately, Jerry himself somehow now has the brain of a lion as he pulls off a rather frightening impression of the MGM lion inside his filmstrip ribbon-decorated mouse hole, sending Tom over the edge so badly that he takes off like a rocket and vamooses away from the castle.
- Silly Animal Sound: The cat who has had his brain switched with the dog now barks and growls like a dog while the latter now meows like a cat. Later on, we also get a tweeting elephant, a bleating chicken and a mooing cuckoo clock. And who could ever forget Jerry roaring like Leo the Lion?
- Stock Femur Bone: Jerry gets one and a can of dog food from his mouse hole and stands on the latter to entice the orange dog-brained cat with the former. When Tom attempts again to convince the orange cat that he is a cat by hitting Jerry, the fido-minded feline retaliates by bashing Tom over the head with the bone, causing his body weight to collapse. He is later seen with the bone in his mouth when he once again stops Tom from chasing Jerry, with Tom holding onto the bone as the cat charges him into a grandfather clock, attacks him from inside and jumps out with him through a window and at the edge of a balcony. As Tom is clinging for dear life onto the bone, the orange cat barks and causes the bone to fall to the bottom, taking Tom with it.
- Squashed Flat: After seeing Tom as a "beach cat" in the "Lovable Cats" book, the orange dog-brained cat closes the book hard, opens it again and flips through the pages, which show Tom flattened onto them. When the cat hears Jerry whistling for him and drops the book to come to him, Tom then opens up the book and operates it like an air pump to inflate himself back into shape.
- What Happened to the Mouse?: The mad scientist doesn't appear again for the rest of the cartoon (although he can be heard laughing off-screen when Tom is running around the castle near the end) after giving Jerry the dog-brained cat as a companion. Said cat likewise also disappears after Tom tries to escape the castle in a panic.
