It is an adaptation of the 1905 short story "Pigs Is Pigs" by Ellis Parker Butler. A railroad station agent in Scotland by the name of Flannery takes delivery of two guinea pigs. Flannery, who is such a prisoner of the rule book that he can't even say hello without consulting the book to see when he's supposed to, decides that guinea pigs must count as pigs for charging freight delivery. When the man receiving the package, one McMorehouse, shows up at the station, Flannery insists on charging the 48 cents fee for pigs. McMorehouse refuses, stating that they are his pets, not pigs, and saying he will pay no more than the 44 cent fee for pets. Flannery refuses to release the guinea pigs for 44 cents, instead cabling railroad headquarters for instructions.
Unfortunately for Flannery, he doesn't count on one thing. Guinea pigs have babies. A lot.
"Pigs Is Pigs" provides examples of:
- All for Nothing: By the time Flannery gets a response from the railroad company, McMorehouse has moved and he can't deliver his guinea pigs.
- Aside Glance: As Flannery was shoveling the guinea pigs, some are flung towards the camera. One of them seems to be looking at the audience and flung back towards Flannery.
- Blatant Lies: The narrator declared the railroad office's bureaucracy was speedy and efficient. The montage that follows showed that it's anything but.
- Blowing Smoke Rings: Flannery at the end, having finally rid his wrecked station of guinea pigs (or so he thinks).
- Bothering by the Book: Flannery is a slave to the rule book. It backfires disastrously after he refuses to release the guinea pigs on the mistaken belief that they are actually pigs.
- Call a Smeerp a "Rabbit": The central joke, that "guinea pigs" are not pigs at all, but small rodents.
- Didn't Think This Through: In response to Flannery's distress, a clever young clerk suggests that the guinea pigs be stored at the railroad's main office station. Unfortunately, he didn't know that they had multiplied to "a million and two".
- Explosive Breeder: The guinea pigs have babies and babies and more babies. They breed from just two to "a million and two." The train station literally explodes from the mass of the guinea pigs. Finally Flannery dumps them all in train cars. He shovels up the last two from the train platform, and they have four babies while in the air. When the pigs show up at the corporate headquarters, the whole building bursts at the seams.
- Eyebrow Waggle: The male guinea pig waggles his eyebrows at the female whenever they're ready to, um... multiply.
- Here We Go Again!: The last shot reveals that two guinea pigs, a brooding pair, are hiding in Flannery's hat.
- Hobos: Such is the Vast Bureaucracy at the railroad headquarters that even the hoboes riding the rails get 24 copies of the report about the guinea pigs.
- Impossible Hourglass Figure: She's only a brief throwaway character, but the Sexy Secretary filing the thousands and thousands of reports about the guinea pigs is drawn with wide hips and wide bosom and a tiny wasp waist.
- Laser-Guided Karma: The railroad's inept and obstructive bureaucracy system resulted in their main station being filled to the bursting with guinea pigs.
- Limited Animation: The short is done with simple drawings and limited animation of the sort that had become very stylish in the 1950s after UPA, the Trope Codifier, had so much success. It certainly looks more like UPA than a Disney product.
- Music Soothes the Savage Beast: In a vain attempt to stop the guinea pigs from reproducing, Flannery serenades them with Irish jigs from his fiddle.
- Obstructive Bureaucrat: Flannery isn't malicious like your everyday obstructive bureaucrat, but his insistence on rigidly following the rulebook, and then asking the home office for instructions rather than just letting the pigs go for 44 cents, leads to disastrous consequences.
- Rhymes on a Dime: All the narration and most of the dialogue is in verse.
- Running Gag: The bird on the telegraph wire, which gets all its feathers shocked off whenever a telegram goes back and forth between Flannery and corporate HQ.
- Screw This, I'm Outta Here!: In response to the millions of guinea pigs crowding the main office station, three officials turned in their resignations.
- Seldom-Seen Species: Guinea pigs, much less seen in animation than other small animals like rabbits or mice. They're fairly well-known today, but were less so in The '50s.
- Tempting Fate: After finally getting rid of the guinea pigs, Flannery sends a telegram to the railroad company joking that at least it wasn't elephants. Then he sees two elephants in a train car eyeing each other amorously, and Flannery faints. Fortunately, the circus train carrying the elephants doesn't stay long.
- Thrifty Scot: McMorehouse, either because he's standing on principle or because he's cheap, will pay only the 44 cent "pets" rate for the guinea pigs, not the 48 cent "pigs" rate. He leaves, and Flannery is stuck with the guinea pigs, who soon fill up the railway station. The customer in the original story was called just Morehouse; Disney added the "Mc" for the sole purpose of invoking this trope.
- Title Drop: "Pigs is pigs!", says Flannery as he refuses to let McMorehouse have them for 44 cents.
- The Un-Smile: Flannery reads the rule in the rule book that says he's supposed to smile for the customer. He plasters a weird rictus grin on his face.
- Vast Bureaucracy: The headquarters of the railroad line. The simple question of whether or not guinea pigs count as pigs for charging freight leads to thousands of reports going all over the company—the president, the board of directors, junior clerks, secretaries, janitors, even the hoboes that ride the rails. By the time the board finally calls in a scientist who confirms that guinea pigs are not the same as common pigs, the two guinea pigs at the train station have bred so much that the station has exploded.
- We Are Not Going Through That Again: In the closing monologue, Flannery declares "No more will be a fool. Whenever it comes to livestock, blast every single rule! If the animals come in singles, or if they come in sets; if they've got four feet and they're alive, they'll be classified as pets!"
- Your Tomcat Is Pregnant: Flannery names the two guinea pigs Pat and Mike but "he quickly changed it to Marie" when he looks in the box and sees Pat and Marie snuggling and four babies in the box. This is the start of his troubles.