The first time it happens, John doesn't even recognise it for what it is.
He is dozing in his armchair, the reassuring sounds of Sherlock in the kitchen working on another ghastly experiment, lulling him deeper into his slumber. When he feels cold slender fingers on his wrist, he thinks he's dreaming, like he did those two hateful years Sherlock was away and he was alone drowning his sorrows and regrets.
So he revels in the dreamlike touch, tilts his hand slightly so his wrist is more accessible. But then the fingers retract and John sinks in a deep slumber.
He barely remembers it when he wakes up to Sherlock's cursing and the sound of breaking glass.
The second time John doesn't notices it.
He dreams. And maybe it's the grey sky hanging over their heads all day or maybe the fact that today they had a crime scene involving a jealous ex, a tall building and a body smashed to the ground – the first had made it want to seem like a suicide – but John is dreaming about that dreadful day when his world came crashing down along with Sherlock's body.
He hears himself screaming his name, tries to run, to stop him, to catch him before he hits the ground, but dammit he is too slow. Again.
He wakes when he hears his own name being called out. The first thing John sees when his eyes spring open, is Sherlock, looking tired and frightened himself, sitting on the bed, right in his sight. He doesn't need to ask what the nightmare was about and John doesn't think he can even say it out loud. For a moment, John hates him again. Hates him for leaving. For not telling him, for not trusting him. But the anger dissipates quickly when John remembers Sherlock's explanation, his near begging for forgiveness. And the fact that he's here, he's right here with me, calms him down tremendously.
When they both have calmed down, Sherlock gives a quick nod and stands without saying a word before leaving the room. John doesn't thank him; he never does. Something the silence is all they both need.
John lies back again and it is only then that he realises that Sherlock had held both his wrist firmly the entire time, fingers on his pulse point. He falls asleep contemplating this and to the sounds of Bach coming from downstairs.
The third time Sherlock claims it is for an experiment.
It isn't the first time Sherlock focussed his enormous brain towards John in a dull moment. John can fondly remember – although he felt less than fond at the time – the time Sherlock was examining John's blood under the microscope in comparison to his own. In fact, John knows Sherlock has an entire spreadsheet on him. How he likes his tea, what time he gets up on average, when and how long he goes out for a walk, how far he can go before John has too leave the flat to cool down – that had not been a pleasant week.
So when they're both sitting at the kitchen table and Sherlock suddenly reaches out to grab John's wrist, John stares only briefly. 'Sherlock, what…'
'Your heartbeat in rest, it's slightly lower than the average male,' Sherlock announces and John finds himself nodding. 'Was it always like that?'
John frowns. 'For as long as I can remember yes, but why…'
'Data, John!'
And that's the end of that.
The fourth time there is no denying it nor the reason behind it.
They have been running on fumes trying to catch a serial killer before he makes his fourth victim. Sherlock and John, side by side, miles ahead of the Yard, entered the suspect's safe house without much difficulty, but inside proved more of a challenge. Immediately on their passing into the large bedroom, a scream distracted them – the next victim, tied up and gagged, but damn she had a good pair of lungs on her – followed by a baseball bat hitting John's gun straight out of his hands. John grabs the bat without thinking and what follows is a scuffle that leads both him and the suspect tumbling down the stairs.
The first thing John feels are the cold slender fingers pressing down at the pulse point on his throat. They're trembling. Next he hears Sherlock's frantic voice. '…wake up…please, don't be dead…come on, John, please!'
'Sh'lock?' John is feeling dizzy and disoriented when he opens his eyes and he quickly closes them again. He loses his consciousness again shortly after.
This time when he wakes up, he feels the fingers on his wrist, despite the fact he can hear the beeping of the heart monitor next to him. Suddenly, with surprising clarity, he understands.
He wasn't the only one alone during those two years. Sherlock left him because a sniper would make him leave Sherlock if he didn't. Sherlock fought and hid for two years, while those snipers were still a threat. John hadn't known. Of course he didn't. It wasn't until Sherlock had returned and John had demanded Mycroft for answers when Sherlock wouldn't give them, that he understood the true motivation.
Your friends will die if you don't.
And with Sebastian Moran, who was right here in London for those two years, still fresh in his memory, who can really blame Sherlock for making sure John hasn't been taken away from him?
John doesn't say anything though. He turns his hand and grabs those fingers. Sometimes the silence is all they both need.
The fifth time is the time John encourages it.
They're breathing each other in, their lips barely ghosting against one another. John feels elated and a sense of finally, finally! is coursing through his veins. Sherlock touches him everywhere at once and it's nowhere near enough. The detective's face is surprisingly fragile and insecure and John grasps his hands without reservation.
He offers his wrist.
Sherlock looks at him with wide open and beautiful eyes and John smiles. Very carefully, he feels Sherlock fingers slide over his wrist and when the rapid beats of John's heart interact with his fingertips, Sherlock's face breaks into a smile.
'I'm here,' John murmurs.
'So am I,' Sherlock confirms before taking his mouth into a bruising kiss again.