Rodents are a grouping of small mammals native to Earth including such species as mice, hamsters, and rats.
Rabbits and hares were sometimes classified as rodents, but are now classified in the order Lagomorpha, a sister order to Rodentia.
The JMC mining spaceship Red Dwarf had mice present in its laboratory, and which were apparently the only non-human entities aboard, besides Frankenstein. The lowest ranking member on the ship, Third Technician of Z Shift Dave Lister, joked to his bunkmate Arnold Rimmer that he at least had authority over the lab mice - if he told them what to do, they had to jump to it saying "yes sir!" in a squeaky voice. ("The End")
Three million years later, Cat hunted a mouse he believed he saw in the cargo bays. Cat tried to coax the mouse out by saying he only wanted to be its friend, and would give it cheese. Cat then lost his patience and began hitting the surrounding metalwork with a piece of wood. Cat was then interrupted by Lister and Rimmer, since they had discovered a signal from a crashed ship, Nova 5. ("Kryten")
The boys from the Dwarf often watched cartoons, one of which was Tales of the Riverbank starring Hammy Hamster. ("Camille")
Tom and Jerry was a series of cartoons featuring a cat and mouse, and in which the mouse usually outwitted the cat which wanted to eat it. Cat referenced these cartoons when Starbug was in a 'cat-and-mouse' game with the Simulant Battle Cruiser. Cat advised his crewmates to strike with the laser cannons instead of running, since the only way to win is 'not be the mouse', 'not unless you believe those lying cartoons'. ("Psirens")
When Ace Rimmer attempted to train his Red Dwarf counterpart Arnold to become a hero like him, he took him into the AR Suite and suggested that Arnold imagine a "cougar running free and unfettered among the mountains". However, all Arnold could imagine was a hamster running in its wheel. ("Stoke Me a Clipper")
When Starbug came back aboard Red Dwarf as it was being reconstructed by nanobots, Red Dwarf was massively enlarged and Starbug got sucked into a gigantic ventilation shaft. As it flew along, it narrowly avoided being gnawed by a giant rat. Starbug then became stuck up the back end of a second rat, taking the rat along for the ride. The Dwarfers could hear the rat's heartbeat from inside the ship. Holly quipped "I hope we don't get pulled over by the cops. They don't like it when you're rat arsed". Starbug took a turn and the rat flew off down another shaft. ("Back in the Red Part I")
When Arnold Rimmer got hold of a Quantum Skipper, he used it to explore various dimensions of The Multiverse. One of these dimensions was one where Lister smuggled a pet rat aboard Red Dwarf instead of his cat Frankenstein, and subsequently the entire ship was overrun by giant evolved rats, Rattus sapiens, instead of Felis sapiens. Cat was instead replaced by The Rat. Rimmer did not stay long in this dimension, or "rat world" as he put it. ("Skipper")
- It is unclear what Cat was hunting in the episode "Kryten" when he was searching for a mouse in the cargo bays. It is possible that it was a descendant of the ship laboratory mice (mentioned in "The End"), although it would seem unlikely these would have been able to survive the radiation leak (Lister's pet Frankenstein was said to be the only living thing which survived, and that was because it was hidden away in the only part of the ship which didn't receive a massive dose of radiation).
- Another possibility is that Cat may actually have been hunting a space weevil.
- When the nanobots restored Red Dwarf to its former state from before the radiation leak, this included a number of rats in the ventilation shafts (see "Back in the Red"). This would seem to suggest that rats had been stowaways aboard the ship from the beginning, and the laboratory mice were not the only rodents aboard.
- Rattus sapiens - a species that evolved from rodents
- The Rat - a Rattus sapiens who is counterpart to Cat in one dimension
- Space Weevil - another critter sometimes aboard spaceships