John moves his thumb half an inch higher and presses firmly.

Muscle quivers, but Sherlock's resolve holds firm. In a throaty baritone comes a haughty "no."

John supresses his smirk and tries again.

This time there isn't even a flinch; Sherlock just shakes his head. His eyes are staring at the ceiling with total concentration; he won't even look at John.

Another quarter inch higher brings him into contact with the dark hairs of Sherlock's axillary fossa. Another push, and John finally gets what he wants – a snorted giggle and a squirm away from him.

John's laughter rings out triumphantly, "I win!"

There is a growl from the other side of the bed. "You're not playing fair."

"You know the saying…"

"What?"

"All's fair in love and war."

"Tickling is more war than love."

It sounds more like a tease than a complaint, but even so, John knows that he's pushing the boundaries a bit. Due to his hypersensitivity, this is a harder test for Sherlock than it would ever be for John. The fact that he's letting John indulge, instead of retreating with a glare, is sobering evidence as to the level of trust they've built. "It's another way of saying that the ends justify the means," John explains.

"And to what end are you torturing me?"

"Because I like to hear you laugh."

There is a rustle of sheet and the mattress creaks. Suddenly, there is an explosion of movement and six feet of tousled hair and ivory flesh has flipped John over and straddled him, pinning his hands down on either side of the pillow.

John looks up into those grey-green eyes, and laughs again. "You do know I am trained in combat tactics?"

"Of course. But after we beat each other senseless and call for an ambulance, we'd end up in an A&E. Where's the fun in that?"

John purses his lips, pretending he's trying to decide. Then he shakes his head. "Nope, I surrender."

Sherlock rolls off him. "Thank God. You get to go make tea." He wraps himself up in the duvet, leaving John exposed to the chill in the bedroom.

John is still smiling when he brings back the two cups of tea. He deposits one on the bedside table on Sherlock's side of the bed, and takes his own to the other. Slipping his feet under the duvet-mummified body next to him, John leans back against the headboard and lets the steam from the tea warm his face. With his woollen dressing gown on, he doesn't feel as cold as he had when leaving the warm confines of their bed.

"You're right, you know. It isn't fair. I have a better understanding of human anatomy than you do. The armpit is almost always ticklish," John muses.

Sherlock pushes aside the duvet he has been hiding under and lifts his head, framed by a halo of curls. Sitting up, he takes a mouthful of tea and then settles his back against the headboard as well. He opens the duvet up so John can share a corner, draped across his lap.

"I should be able to control the reaction. It's merely a fight or flight reflex, caused by pressure being applied to a body's most vulnerable places."

John smirks into his tea. "Sherlock, even you can't ignore millennia of human evolution. Some things can't be controlled, no matter how smart you are."

Sherlock isn't placated by this. He puts an exaggerated pout on his face. "Now that I'm awake, you may carry on with the experiment. I've read that the armpit is supposed to be an erogenous zone. How can that co-exist with the tickle response? Care to show me?"

"Your tea will go cold."

Obediently, Sherlock picks up the mug and drains it. "Ready when you are."

Once John has finished showing Sherlock just how the same spot can, indeed, be both ticklish and erogenous, they both need a shower. He decides to let Sherlock have the first one, because they have come to realise that making love in the shower is not as straightforward as they might like. The shower being over-the-bathtub plumbing means that one of them will freeze while the other hogs the stream of hot water, and John generally loses out. Practicality means that when the emphasis is on cleanliness, it's best to take turns. John is looking forward to summer, when issues about the temperature of the room and water in a shower will no longer be factors to be considered important in their sex life.

As he listens to Sherlock moving about in the bathroom and the water in the pipes rattling its way up from the boiler in Mrs Hudson's utility room, John lets his thoughts drift to what the past weeks have meant. This morning has been just one example of the unexpected consequences of being Sherlock's lover. Never, not in his wildest fantasies (and he'd had some that still make him blush) had he ever once thought that sex with Sherlock would be what it has proved to be.

Fun.

The thought makes him smile. So many times, he'd worried about what it would be like to make love to a man, without realising that it was more of a footnote than the gist of the issue. This is Sherlock, not some hypothetical unknown male. It was always going to be different, and it wouldn't have mattered if John had amassed bisexual experience to earn him the soubriquet of Three Continents Watson with both genders; he should have realised that Sherlock would be unique.

There is Sherlock the sex researcher who is fascinated to find out just how quickly he can make John come, or how long he can drag it out before exhaustion overcomes libido, and they both collapse into a sweaty heap. John has been on the receiving end of some experiments that he hadn't even realised were taking place. A good example was the events of last week: in order to keep his erection from becoming noticeable to Sergeant Donovan, John had been forced to imagine doing the autopsy on the dead body they were hunched over at a crime scene. The reason for his predicament: the way Sherlock had been looking at him all morning, unabashedly letting his eye wander to certain parts of John's anatomy. It wasn't until they were in a taxi, heading home after they'd solved the case that Sherlock finally admitted that he had been trying to see if he could get John so excited that he would snog him senseless in front of the Yard.

Open-mouthed in surprise, John could only manage: "I sort of thought… you know, that unwritten rule of yours…"

That had made Sherlock look up from his phone. "What rule?"

"You know, that no food or sleep during a case –thing, I thought it would also include no sex."

"Why on earth would that happen? Sex doesn't slow me down; you have turned out to be the most powerful stimulant known to me that isn't a class A drug."

John had giggled. "Well, that's one addiction I don't mind you having."

He had then thought about Sherlock's habit of totally ignoring social conventions. "Does this mean that a bit of PDA might become a habit then?" John tried to imagine the faces of the Yarders if he had succumbed to the temptation.

That had made Sherlock look up again and put away his phone. He faced John with a look of total confusion. "PDA? What do Patient Dispensed Analgesics have to do with this?"

John had laughed, "No, I meant public displays of affection."

Sherlock opened his mouth to say something, but then stopped, and his frown intensified. "Does the notion bother you?"

John had shaken his head. "Not at all. Just wondered if you thought it might damage your professional image as the world's only consulting detective and established sociopath."

The smile had returned to Sherlock's face. "John, if I can deduce exactly how long it's been since Anderson and Donovan ended up in bed, or that Lestrade's been kicked out to sleep on the couch by the adulterous wife of his yet again, don't you think that it's only fair that they can see that we are fulfilling their expectations? I couldn't care less about their opinion; all I care about is what you think."

John had shown him exactly what he thought, as soon as they got behind closed doors of their flat. That night, their lovemaking had ended the way it usually did – with John sprawled across Sherlock's chest, sound asleep.

He'd apologised the first time it had happened, saying it was hardly polite to crush a partner like that.

The baritone rumble of mirth had surprised him. "When I was a child," Sherlock had explained, "my mother gave me a weighted blanket, because the pressure helped me calm down and sleep. You are an infinite improvement – a model with a built-in hot water bottle."

John swallowed, acutely aware of how little Sherlock talked about his childhood or about the fact that he had always needed certain routines and habits to manage in the world. "Friends with benefits, eh?"

More often than not, that is how they sleep now – Sherlock on his back, with John using his chest as a pillow. For years, John had avoided close contact with anyone in a bed. Maybe it was the years of a single army camp bed, but he'd almost always excused himself from a woman's bed to find his own place to sleep. Sex was one thing, but staying the night contained a level of domesticity John had always, somehow, been uncomfortable with. Maybe it was because none of those women had felt exactly right, somehow. After being shot, he'd struggled to find the right position to put pillows around him to help brace his left shoulder. Draping it over Sherlock's chest, and nestling his head onto the man's ribcage was the perfect solution. They fit together, in a way that John had never anticipated, especially considering Sherlock's height. If he woke in the night now, the contact eventually meant that their breathing patterns would match and somehow the synchronicity of it would send him back to sleep.

He had not had a single nightmare after moving into the downstairs bedroom. The same could not be said for Sherlock, but he had told John that having someone right next to him helped. The restless nights were becoming a rarer occurrence, but they still happened, and John was happy to help, holding Sherlock in the dark until they both drifted off again.

There is a faint but very familiar scent now wafting its way into the bedroom through the bathroom door. It's Sherlock's shampoo, and John has come to love the aroma, now that he can bury his nose at will into those curls of his. He has relished the opportunity to get to know every nook and cranny of that body. What had once been mostly concealed under perfectly tailored clothes was now his to touch and admire.

The reverse is true, too. He's become aware of Sherlock the forensic investigator, who has clearly decided that John's body is his own private playground to explore.

Take last night, for example.

"John, did you know that the taste of your skin behind your ear is very different from what my taste buds register just here?"

That oh-so-talented tongue had been exploring John's sacrum at the time – that tiny triangle of bone at the base of his spine which John had ever paid much attention to before. The sensation had sent electric shocks up his back and down, too, getting yet another rise from something that had already had its fun. This had been supposed to be a lazy, post-coital embrace, but Sherlock seemed to be attempting to spark another round.

John had reciprocated by licking the long fingers he managed to finally capture against the bed. "You taste of lemon. Why?"

"That's because I haven't washed my hands yet. We had chicken jalfrezi for dinner, and I squeezed a lemon wedge on it. Does sex affect your deductive capacity? It has the opposite effect on me, I wonder why?"

"You tend to have paradoxical reactions to a lot of pharmacological things, maybe that applies to endorphins and oxytocin as well. Most people just bliss out at this point and go to sleep."

"Boring."

Speaking of which, it was a word John would never use to describe making love to Sherlock. In all his previous sexual encounters, there had always been… well, not to put too fine a point on it, rules. And routines. Usual sexual etiquette meant that there were certain things that were done — or not done— in the early stages of a relationship. And, since John had never managed to sustain a relationship for all that long, sex had been pretty predictable. No one wanted to frighten the horses by being too kinky when things were still a bit unclear about where the relationship might go. Most of his dating habits led pretty quickly to a bedroom scenario, so it wasn't as though he had a significant amount of time to get to know the other person before they ended up naked. So, he'd worked diligently to ensure that his female partners were getting as much gratification out of things as he was. That led him to focus on technique, and he'd grown adept at it. Because he knew that the female orgasm was a lot about what was going on in the mind, he took things in the bedroom slowly to let whatever fantasies they needed take hold and drive his partner to a climax.

With Sherlock, it was the opposite. He had to get the man to stop thinking, in order to surrender to the feeling. For once, John wasn't the one who had to worry about coming too soon. Once Sherlock had experimented enough, he knew just how to manage things so that simultaneous orgasm wasn't the rare coincidence it had been for John with a woman; it was a bona fide target. John had never appreciated just how Sherlock's perfectionism would translate into what happened in a bedroom. His pursuit of every sensation, every conceivable pleasure to be derived from sexual contact was yet another aspect of the amazing man.

Sherlock's assertiveness was another surprise. John had assumed that because he was the more sexually experienced one, Sherlock would tend to defer to him, letting him take the lead. That had not proved to be the case. Once past the initial hesitancy – once Sherlock had realised the effect he could have on John – he was more than happy to initiate, and even lead the way. He was no shrinking violet when it came to letting John know just what was working for him.

He'd bought a pair of earplugs for Mrs Hudson, who just laughed at John when he delivered them to her. "Don't think for one moment that I haven't heard that sort of thing before. It makes me smile, the sound of the two of you making up for lost time."

They had their quiet moments, too, when just a touch on a tense shoulder or a hand on a knee was enough to steady a fidget or calm a temper. Non-verbal worked for both of them. John had learned that he didn't need to resort to silly "sex talk"; he still cringed a bit when he recalled his use of the phrase "I'd like to take you apart", a little gem picked up from one of those ridiculous porn films that he'd been watching to try to get some pointers. Every time some clichéd word came to mind, he remembered how Sherlock had reacted to that comment by withdrawing, so he stopped himself from repeating that sort of mistake. He no longer needed to rely on other people's ideas about how to talk about sex; they had found their own language. A raised eyebrow, a quirk of a lip in a particular way was now enough.

The sound of the hairdryer tells John that he has about another seven minutes to wait. He slurps the last of his tea, and pulls up to his chest the rest of the duvet that Sherlock had discarded.

It smells of sex – no, not just sex per se: it smells of them, and it brings a tightness to his chest, the thought of how much he loves Sherlock. John's own hesitations had once been enough to stop him from thinking that openly loving Sherlock was even possible. He'd had no idea what Sherlock's attitudes might be towards sex with anyone, and Sherlock had made his stance on relationships quite clear, even though all that had turned out to be a load of rubbish, an excuse to keep others at bay because Sherlock didn't want to take a leap of faith that carried a risk of pain.

John had spent years telling people they weren't a couple, that he wasn't gay, that he didn't think of Sherlock in that way. Even when the events that landed Sherlock in the hospital proved how wrong he had been about that, it had been a gradual process to accept everything that a proper relationship would entail. At first, he hadn't even really wanted to think about the practicalities of having sex with Sherlock. They had both needed time to process things, but the timing had, of course, been disastrous. Him, alone at Baker Street. Sherlock, stuck at a posh rehab in the countryside with too much time on his hands to worry and lose what little confidence he had. They'd come a long way since then.

Before it had actually happened, John had worked himself up about his lack of experience with the technical aspects of what gay men did when making love, basing his thoughts on what online pornography he could stomach. This brand new territory appeared to be full of its own rituals and expectations, different from those he'd developed with women. It seemed that the internet presented him with a whole new lexicon and rulebook, with stuff like tops and bottoms, rimming, subs and doms. It made him worry; if Sherlock expected him to take the lead, he was going to find all this quite challenging.

He shouldn't have worried. For starters, he'd been overthinking the whole thing – maybe he was picking up bad habits from Sherlock. Both of them were exploring things that neither of them had experienced before. With Sherlock, there was no routine; he wanted to try everything with the open curiosity of a scientist, never basing any assumptions on what they should or should not be doing. And, he was more than capable of deducing John's reactions, which was a godsend. No more tentative questions that John's female partners had always posed along the lines of 'what are you thinking?'. John had always felt put on the spot by such things, leading him to invent things or to fake delight to keep his partners happy.

After one particularly athletic endeavour, John had asked Sherlock if he'd enjoyed it.

That raised the crinkled lines between those eyebrows, the look that John loved because he enjoyed being able to surprise Sherlock. "Why do you think I would do something I didn't enjoy? When have I ever done something I didn't enjoy? I don't have to ask you whether you enjoyed it; the evidence is all over the duvet, which we are going to have to get dry-cleaned yet again."

Making love to the women that had drifted in and out of John's life had always been done gently, carefully; almost politely. He knew that if he got carried away, then his partner might suffer the consequences, and he never, ever wanted to hurt anyone. That was so not his scene.

But, with Sherlock, muscle was matched by muscle, and neither of them was fragile or delicate. Sherlock's hyper-acute sense of touch made too gentle a gesture overwhelming, so John had to re-calibrate his habits. And, he found that he liked it, not having to hold back as much. This was yet another reason why making love to Sherlock was so completely different an experience to anything he'd ever enjoyed before.

Once he got past the first-time jitters, John had come to realise that there actually weren't that many differences in anatomy. Breasts might not be the same, but nipples certainly were in the sense that stimulation had a very similar effect with both genders. And, mutually enjoyable penetrative sex, regardless of the precise anatomy involved, required preparation and was still a case of insert tab A into slot B. Oh, and by the way, both genders had a slot C for the orally creative approach. And even a slot D, if intergluteal sex was counted.

John's haphazard online research had failed to illustrate that there was no presumption that sex had to involve penetration of any kind. Sex with a man had surprised John by just how many different variations of a theme were possible. Sherlock seemed to have erogenous spots that most people utterly ignored. Being less able to filter out the random contact of clothes against his skin, or sights, sounds and scents meant that there were things John could do to him that would not be even remotely titillating to most people.

It all makes John smile. What had turned out to be the worst of Sherlock's worries – the fear of a meltdown caused by too much sensory information – had turned out to be not much of an obstacle at all, when he was in the hands of the right partner. John's sensitivity to him, the knowledge he had amassed during years of just living in close proximity to him, meant that he was well attuned to the limits beyond which he mustn't go.

This required an intimate understanding of each other, the likes of which John had never experienced with anyone. Before, sex had come along rather soon in his relationships; now, everything was built on the sturdier foundation of friendship and gradually constructed emotional intimacy. Before Sherlock, John had equated the word intimacy solely with sex. His relationship with Sherlock had proved him wrong about that in ways he had never understood until lately. Whatever regrets he had about not acting on his feelings until so much time had been wasted, John is grateful now that he didn't rush things. Had they jumped into bed during the early stages of their relationship, John is convinced that he would have probably made a lot of potentially disastrous mistakes.

The bathroom door opens and Sherlock walks in – totally naked, pink from the hot water – and slides back under the duvet again. Soon, a baritone muffled by a pillow mutters: "We need to change the sheets."

John groans. "Again. I'm getting tired of doing the laundry so often."

"We could get a service. Fresh sheets delivered daily; a clean duvet every week."

"That's expensive."

"I'll just take a boring case to pay the bill."

John sniggers. "The sacrifices you have to make."

"You're worth it."

That says it all, really. Everything they've been through, even all the pain, to get to this point.

All worth it.

Author's Note: This is part of the "On the Rack Extras"- a series of One Shots that are part of the On Pins & Needles Series. If you haven't already done so, go read J_Baillier's "Inherently Given" and "A Lighter Kind of Loneliness". And be patient, 2007 is coming.