Two notes: 1) my rat totally wags his tail, and 2) writing the little death scene made me cry *is dork*
A Boy and His Rat
Remus Lupin hadn't ever had a pet, for what he felt were obvious reasons. He claimed he was allergic, even though he'd never sneezed once in collective Marauder memory.
James Potter showed up for his first day of Hogwarts with a brand new, glossy brown owl. The owl, whose name was unfortunately Claw, brought James dead mice at breakfast sometimes and would detonate Howlers outside before bringing in the mail. Claw lasted longer than any of the other boys' pets, lasted the whole way into James' marriage, and when he finally keeled over after bringing in the paper one last time, James buried him in the backyard and refused to buy another owl. Since it wasn't safe to use the Owl Post by then anyway, no on argued with him.
Sirius Black had a long and illustrious line of pets during his Hogwarts career, all varying amounts of poisonous and legal. Some of them blew fire, some of them glowed in the dark, many of them escaped, more than one found its untimely demise in Snape's potions cauldron. The best pet, by general consensus, had been the tiny pink squid he'd brought back from a beach holiday, which had gotten so large that by spring it was residing permanently in one of the Gryffindor shower stalls. When McGonagall had found out, all four boys had snuck out in the dead of night to release the squid into his new habitat, Remus humming 'Anchors Aweigh' as it waved a slick tentacle in farewell and slipped beneath the lake water.
Peter Pettigrew had a rat.
When they'd shown him the rat in the pet store, he'd been skeptical, but when his sister had skipped up to twist his ear as usual and discovered the rat on his shoulder, she'd screamed loud enough to make wizards drop to the floor in fear of attack, and Peter'd been sold.
During his first trip on the Hogwarts express, when three Fifth Years cornered Peter and bloodied his nose for his trolley money, the rat waited until a dark-haired boy in thick glasses was helping Peter up before trotting back out of the corner he'd been lurking in.
"Your pet's just as useless as you are," another dark-haired First Year sneered, but Peter scooped up his rat quickly and put him back on his shoulder.
"Is not," he snuffled, voice thick because of the nosebleed, "he's smart. I would've gone and hid until they were gone if I could."
Peter Pettigrew lacked imagination, so his rat was simply named Rat, but Rat could pick out which Bertie Botts you should avoid, and their room never had mosquitoes because Rat would hunt them, and if Rat scurried off the potion's desk suddenly you knew to get the hell back from the cauldron because an explosion was nigh.
Sure, other people had flashier pets, or more dangerous pets, or pets that were good for spells (and Peter could've used all the help available), but James' owl didn't share Chocolate Frogs with him in the middle of the night after a nightmare, and Sirius' Miniature Spitting Snorfler didn't sidle up next to him on the couch and roll over to have his belly scratched.
Rat knew that you should always stash away some of the Cockroach Clusters somewhere safe, because you might not be able to get to the kitchens next time you were hungry. Rat knew that leaving a warm bed before 8 am was completely unreasonable. Rat knew that when people who were bigger and meaner than you were shouting, the best thing to do was to hide until it was quiet again.
But Rats don't live forever, and Rat seemed to know that too. During the winter of their Fourth Year, Rat spent most of his time taking naps on Peter's lap, waking only to nibble on bits of food that Peter offered him and lick the back of Peter's hand before going back to sleep.
And early on a morning that smelled like spring wasn't far off, Peter woke to find Rat curled up in his usual place on the pillow, paws held close to his chest in tiny fists and stone cold. Sirius, who had been merciless when Peter cried because his elbow'd been snapped the wrong way during a broom-riding accident, didn't say a word when Peter wiped his sleeve across his eyes the entire time James and Remus were burying the pencil box in the half-frozen dirt directly below their dorm window.
When James and Sirius were whispering behind Remus' back about becoming hippogriffs and dragons and basilisks and every other creature with teeth and claws, Peter remained practical and recalled that being big and scary meant that other big and scary things tried to eat you, and that running and hiding was much safer.
He was the last of the three to manage the change, and the least sure of what he'd turn out to be. He stood in the center of their room with his eyes squeezed tightly shut, hands clenched into fists with concentration, and just when he thought he should give up, he felt something start to give and his muscles twist under his skin in ways that made him a bit queasy.
When he opened his eyes, everything was in shades of grey, but Peter could see the delicate paws on either side of his nose well enough, and he felt the long tail trailing on the stones behind him twitch happily.