Sherlock Holmes does not do pets.

There are things you need to do, when you own pets. Feed them. Water them. Clean their cage. Get them to a vet when they're sick. It's all part of the big one, the main one: pay attention to them, consistently, over time. That's the one Sherlock fails at.

They decide the kitten isn't his fault. He couldn't possibly have known, they murmur, only three. It does take him a while to understand, and he argues for ages about the fairness of it, but when he finds out that the kitten is never coming back, the idea is horrifying. It's his first encounter with death. For years he silently blames himself for loosing the argument. If he had won, then the kitten could have come back.

He does not want another pet. He tells them this. They try anyways. There is an entire Discussion about this. Something small, something with a fixed diet, something in a contained environment so it can't get out and accidentally eat something it shouldn't. Something easy and, preferably, cute. Hamsters.

He tries, really he does. He's fine, just fine for days or weeks or even sometimes months, but then something else comes along and he's distracted and one day he goes and looks and hunger is an amazing thing, because one hamster has eaten the other and is going to work on its own legs and Mycroft has to help him hide the evidence in the garden, or mummy will be Very Upset. He gets enough of a a lecture from Mycroft to make up for it, though. But - hamsters can be cannibals when they are desperate. New data, to console himself with. (She finds out anyways eventually. Mummy always knows. Sherlock thinks the second lecture is just unfair, considering.)

It's somewhat more difficult to get attached to fish. Granted, the Beta had a lovely personality, and he was quite entertained for a few weeks by training it to come to the top of the talk when he had food. But the stuff that grew on the Beta's sides when he didn't clean the tank, that was alive too, and it was fascinating under the microscope. He made the argument that all living things were pets, even the algae and bacteria. It didn't go over well. They removed the tank and refused to let him keep the samples from the little skeleton.

They tried a plant. He insisted it be carnivorous, at the least. It desiccated quite nicely on his windowsill when they went on holiday. He hadn't wanted to go on holiday at all. Somehow, he was still to blame.

He grew up and left. There was a dog, a scruffy mangy awful thing with sharp teeth and big eyes and matted fur. He thought it looked quite fierce. Independent. He wasn't going to make it a pet. Just a few scraps, and only because it looked so hungry. But he underestimated its loyalty, and it needed him so much, and he got tired of it following him around. He was a little relieved when it got kicked by his dealer and broke some ribs. It lived (so did the the dealer, unfortunately). He got it to a vet - and they found it a home through a rescue shelter. No longer his responsibility. No longer a burden. No longer a potential failure but a past failure. He doesn't miss it. He's quite sure it has a much better home somewhere with children who love it.

So that's why he can't have a pet. Or a relationship, really. People have to understand that they cannot, under any circumstances, rely on him. He is not that person. He is not steady, or dependable, or invested or whatever slang the counselors are throwing around which all mean the same thing.

What he needs then is something that takes care of itself. Something that doesn't need him at all but which will still be there when he wants it. After a long study of various creatures he considers a cat (common and completely out of the question for reasons he will not look at too closely) or perhaps a tarantula (initially entertaining, but short-lived and ultimately pointless). Instead, he gets John Watson.

He's very careful to make things clear from the start. Begin as you mean to go on, and all that. John mustn't misunderstand him, mustn't begin to think Sherlock is going to go changing even a little bit just because there's another person in the flat. Just because of the mandatory intimacy of living in a couple shared rooms. Just because Sherlock can sometimes be nice. John should never expect it.

So Sherlock leaves him at the crime scene and does not look back, not even once. He has things to do. John will stay, of course, and there will be a rough bit where he's annoyed at being abandoned, but it's very necessary that he learn straight away that Sherlock won't slow down at all for someone else. (The bit where they're chasing the cabbie doesn't count. Heat of the moment, he forgot he was supposed to be training John. One slip-up doesn't matter.) And it can't just be Sherlock explaining this, John has to know it in his bones. It's one of the most common failures in training a pet: you can't say one thing and do another.

John does not take up much space. He has very nearly nothing to move in with. Jumpers, jeans, stripy shirts, gun, laptop. Nothing much there at all. He fits compactly into the room upstairs and barely uses up any fridge space at all. His things do not litter the living room or get confused with Sherlock's things. Sherlock is so braced to fight off an incursion into his life that the complete lack of incursion is unsettling. John has not marked his territory here. He has not forced any alterations, except the bit about biohazards in with foodstuffs and the bit about caustics in the plumbing and those are intangible. Does the lack of a request for tangible alteration mean something? Does it mean he's not settled in here, not really making it a home? Is it like living in a barracks, a temporary thing?

He steals John's laptop. Repeatedly. This is not related to that, he thinks to himself, irked. Not related to John treading so lightly in Sherlock's life that he hasn't seemed to make any footprints at all. That's what Sherlock wanted, really. Right. This is just him being 1) curious and 2) testing and 3) lazy (know your own faults even if you deny them quite vocally to everyone else). Also training; John must, straight away, get used to the fact that Sherlock will not respect personal boundaries.

John does not need to be entertained. Does he? After Sherlock spends three days on the sofa, he only seems concerned about Sherlock's health. John entertains himself rather well, actually. Sherlock gets bored long before John does. John even attempts to help him find a new case.

John does not make much noise. He does not sing or have parties or play the telly loud or much music or insist on conversations. He sometimes yells, but everyone probably does that when they use the wrong pepper grinder and end up with dried maggots instead of pepper. It's not his fault. The pepper grinders were on sale. It was thrifty. Who cares that they look alike? Should he have spent more money on something just to get it in a different colour? The one with the maggots was on the kitchen table where the experiments go, the real pepper was by the stove where it always sits. John overreacted. Obviously. But when he's not yelling, John's silence is companionable. It means Sherlock can feel free to play the violin whenever he wants without making a compromise. So he does.

It's not relief he feels when John asks him to keep it down at 3 am or change tunes. Not really. More like pleasure at a hypothesis being right. John is human and eventually he will ask Sherlock to make things different, just like everyone else.

Sherlock finds that making things just a tiny bit different with regards to the violin is, perhaps, worth considering if it will mean not finding another flatmate.

John does not seem to get sick. This is probably because he has a strong immune system from being a doctor and getting vaccinations and traveling to odd places with curious diseases. It's good Sherlock never has to nurse him. Sherlock is a terrible nurse. He's been told so by Mycroft. Apparently some cures (such as garlic and cayenne pepper and salt in a liquid suspension for nasal lavage) are worse than the disease (sinus infection). When Sherlock gets sick, John tucks him into the couch with a pinched look of amusement and, as long as he drinks liquids and takes his medicine, John leaves him alone. As should be expected. John is a doctor. Of course he's good at this.

John does not seem to expect to be fed. He'll eat takeaway, or at Angelo's, or any of a dozen other things Sherlock likes, but he seems to feed himself quite well. In fact, gradually Sherlock finds himself eating things like a risotto with vegetables or some apple slices or some other oddly healthy thing, and he realizes that it's John sneaking these things into his diet. It's not as though there were anything wrong with what he ate beforehand.

He dresses terribly, but does not appreciate begin assisted in this matter. (Sherlock what the bloody hell are you doing in my room at this hour? What - I like that jumper, leave it be, stop going through my closet! What's gotten into you? No, Sherlock, we are not going clothes shopping. Now go away and let me sleep.)

John does not need to be cleaned up after. He does not make messes. He cleans up after Sherlock, though. Sometimes. When it's not a large mess and the smell isn't too bad. For example, when Sherlock is in the kitchen barefoot in the midst of the broken remains of an Erlenmeyer flask, John will tell him to hold still while he grabs some slippers and brings them over, then he might stop and help out for a bit. Or when there's an exceptionally large number of crickets involved and they chirp all night, he might help Sherlock collect them again. But they can't go back in the tub. That's where they got out from in the first place. (Crickets aren't pets. They only live a few months. John is not amused by the idea of something chirping for a few months. Sherlock attempting to explain that the stridulation doesn't last for more than a few weeks does nothing for his temper.)

John still follows him around. John comes when he is called. John does not need a single thing from Sherlock except, possibly, those things which are inherent to Sherlock, things which he could no more cease to shed into the atmosphere that he could cease CO2 exhalation. John is a perfect pet.

John's face is a scrunched tissue. It is a map of the world, all mountains and rivers. It is a mouse face, with big ears and a twitching whiskers. It is British with a capital B, a tea-drinking pint-consuming mouth, a nose that appreciates a nice sprig of lavender and a curry, a pair of eyes that scrunch in the sun. John could have fought in any war in British history, Sherlock thinks, looking at him. He can see John in Africa fighting in the Boers, in India, in France and America and Ireland. Steady John. Solid John. Dependable John. Reliable John.

John who feeds him and cleans up after him and finds him a vet and does not let Sherlock doe of dehydration no matter how he tries.

It takes him an unconscionably long time to come to the realization that John is not the pet in their relationship. When he does, he wishes rather viciously, just for a moment, that he had an excuse to take care of himself for a bit. Alone, away from John. Just to prove that he does not need someone fussing over him, reining him in, being a caring and considerate owner. But it's just a passing fancy and just a moment, gone and mostly deleted before he even really thinks of it.

When the opportunity forces itself into playing out, just as he desired, he remembers. And finds does not like the idea anymore.

Not at all.