Harry Potter, Severus Snape, and their environs are the sole property of those who are paid for their literary and cinematic exploits. I own none of that. I do have a wiener dog, a parakeet, an African grey parrot and a Rosebreasted cockatoo, all of whom may pop up in a story now and then. I do not have a cat.
Harry Potter had always been, at heart, a dog person. His favorite professor had been a werewolf, his godfather had been a scruffy mutt animagus, therefore, it was understandable that Harry would gravitate towards canines as companions. Dogs were fiercely loyal, dogs were fearless, and dogs loved to play, the more physical the play, the better. Their barking was a celebration of life, and after the defeat of Voldemort, Harry Potter was going to celebrate life. With Severus. And a dog.
Severus Snape was decidedly a cat person. Cats were stealthy, cats were fiercely independent, cats were fastidiously clean and were very discriminating with their affection. Cats suited Severus right down to the ground. That cats earned their keep by controlling the resident dungeon rodent population was the argument Snape used with Harry, when he brought home a tiny, pure white, half Persian/half Kneazle cat he named Orion.
"Harry, come into the kitchen, I have a surprise for you", Snape called out as he held out a small, meowing bundle that was cradled in his cupped hands. Creeping into the kitchen with some trepidation, as Severus' surprises often involved the threat of explosion, noxious gas, or corrosive chemicals if Harry was not hyper vigilant; he stopped dead in his tracks when he spotted what appeared to be a miniature Pygmy Puff.
"Sev, what is that?", Harry uttered, barely above a whisper. "Please, Sev, tell me you didn't get a cat. You know I'm allergic to cats"-
"You know, there are potions for that", Snape countered, as he held out the little kitten for Harry's perusal. "This is Orion, the Mighty Hunter. He is the ecologically friendly solution to the rodent colony that is occupying the dungeon", Severus proudly proclaimed.
Harry answered his proclamation with three rapid-fire sneezes. Orion responded by scurrying up Harry's right arm to his shoulder, then shimmying up his neck, scratching every bit of exposed skin on the way up, before perching on his head, claws fully unsheathed. "Holy Hippogriff, Sev, that's not a cat, that's a flipping tiger, and he's out for blood", Harry screeched as Severus gently scooped the frightened kitten from Harry's smarting scalp.
Snape was having none of what he considered to be Harry's melodramatic whining. "If you hadn't sneezed, you wouldn't be in this predicament. He's just a kitten, you frightened him. Like it or not, this cat is now ours, and you will care for him as if he were your treasured pet", he said with an air of finality that Harry knew, from vast experience, meant that there would be no further discussion.
Harry gave the fuzzy little interloper his most intimidating stare, which the half-Kneazle answered with an evil smirk and a wink, before emitting a most pitiful meow. "Harry Potter, the Boy Who Frightens Defenseless Kittens, cease your petulant display at once!, Severus snarled, as he carried the scheming little ball of fluff to the cat bed awaiting him in the Potter-Snape living room.
Following a few steps behind his husband, Harry spoke directly to the cat, inaudible to Severus, but loud enough to be heard by the creature that he now knew to be his archenemy. "I took down the likes of Moldy Voldy, and I will defeat you, you malevolent bit of fluff. Your cuteness has no power over me". Harry then waved his wand over the little feline, proclaiming "In honor of your first blood letting, I hereby dub thee Sir Scratch a Lot. May you do the title proud."
Snape's eyebrows arched so high that they almost disappeared into his hairline. "Potter, if you hexed my cat, you'll rue the day you first darkened my doorstep!", he snapped as he dropped to his knees and inspected the kitten, from head to tail.
"Sev, I rue the day I darkened your doorstep every time a cauldron explodes in Potions, or the house elves refuse to make our bed for a week after you, once again, try to bully them into making perfect hospital corners, and every single time you grade the first year's Potions essays. In short, you no longer scare me, although I assure you, all I did now was bestow a title that can best be described as truth in advertising. Your new familiar is safe with me, love, let's get him settled in, and tomorrow, you can start training your cat to do what thousands of years of selective breeding have designed him to do - kill mice. And Severus, I expect a daily supply of allergy relief potion, and it had better be more palatable than your usual offerings. I mean, seriously, do you aim to make your potions taste the way eau de Baboon's Bum smells, or is that just a happy coincidence?"
A bolt of crimson red struck Harry's posterior, simultaneously vanishing his clothing below the waist, and adorning his bum cheeks with a brilliant vermillion hue. "So, Harry, how does a baboon's ass smell?", Severus sneered.
Not to be outdone, Harry upped the ante. "I don't know how it smells, but I'm told that it tastes like chicken. Wanna find out?".
Severus Snape never backed down from an academic challenge, the appropriate research would have to be done. He found that that it most certainly did not taste like chicken, and he followed that discovery with the confirmation that the canine contribution to the catalog of sexual positions was proof positive that the dog was indeed man's best friend. Having conducted said research on the sofa, in full view of the shell-shocked cat, made Harry's ecstasy that much sweeter.
Harry - 1, Sir Scratch a Lot - 0, Doggy Style - 1000. Harry had always been a dog person. In the not so distant future, Severus would come to realize that was not necessarily a bad thing. And what of Sir Scratch a Lot? That, dear Reader, is a tale for another day.