The common rat is a non-magical rodent found throughout the wizarding and Muggle worlds. They are one of the animals students are permitted to bring as a pet to Hogwarts School of Witchcraft and Wizardry, though they are generally less popular than an owl or a cat. Parts of rats, such as their spleens and tails, are also used as ingredients in various potions. The most significant rat in the series is Scabbers, the long-time pet of the Weasley family, who was revealed to be the unregistered Animagus Peter Pettigrew in disguise. Through this character, the seemingly mundane rat plays a pivotal role in the exposure of Sirius Black's innocence and the eventual return of Lord Voldemort.
This section primarily details the history of Peter Pettigrew during his twelve years living as a rat. After betraying James and Lily Potter to Lord Voldemort, Pettigrew faked his own murder, killing twelve Muggles in the process and framing Sirius Black for his crimes. He cut off his own finger to complete the deception before transforming into his rat form and disappearing into the sewers. He sought refuge with a wizarding family, eventually becoming the pet of Percy Weasley, who named him Scabbers. After Percy was made a prefect and received an owl from his parents, Scabbers was handed down to Ron Weasley. For twelve years, Pettigrew lived as Scabbers, first at The Burrow and later at Hogwarts. During Harry Potter's third year, Scabbers's life was made difficult by Hermione Granger's pet cat, Crookshanks, who instinctively understood that Scabbers was not a true rat and repeatedly tried to attack him. After an apparent attack, Scabbers faked his own death once more, leaving a few drops of blood to frame Crookshanks. He was later discovered hiding in a milk jug in Rubeus Hagrid's hut. Scabbers was exposed after he bit Ron and attempted to flee, only to be intercepted by a large black dog, who was Sirius Black in his Animagus form. Dragged through a tunnel beneath the Whomping Willow, he was taken to the Shrieking Shack. There, Sirius Black and Remus Lupin used a spell to force Pettigrew back into his human form, revealing his true identity. Pettigrew later escaped their custody when Lupin transformed into a werewolf and fled. He subsequently reunited with Lord Voldemort and was instrumental in his rebirthing ceremony in the graveyard of Little Hangleton.
The common rat is a small rodent. Scabbers, however, was described as a particularly large, fat, grey rat who looked extremely battered. He had a bald patch on his back and a distinctly chewed-looking ear. His most notable feature was the missing toe on one of his front paws, which corresponded to the finger Peter Pettigrew had severed to fake his own death. As Scabbers, he was generally portrayed as lazy and listless, spending most of his time sleeping. Ron Weasley often complained that he was a “boring” pet. This lethargy was a deliberate act by Pettigrew to avoid drawing attention to his unusually long lifespan for a common rat. In his human form, Pettigrew retained several rat-like features, including small, watery eyes, a pointed nose, and a squeaky voice.
The word “rat” is derived from the Old English “ræt.” In modern vernacular and literature, “to rat on someone” means to betray them by informing on them to an authority figure. The term “rat” is also a common insult for a traitor or coward. This perfectly mirrors the role of Peter Pettigrew, who betrayed his friends to Lord Voldemort.