It hadn't been anything in particular. Not the way Sherlock had wrapped his arm around him and tugged him to sit in that chair that was too small for two as he'd gone to make more tea, so now the empty cup was sitting beside the book, or the warm weight of his cheek pressing against his shoulder that had done it. He'd bored of the book a while ago, and unlike Sherlock, he couldn't have given an exact moment that it had happened. John's eyes flickered towards the page now and then, skimming a few words before sliding down to the way Sherlock's thumbs curled around the corner of the page so it didn't obscure the words, because even pausing to move his hand was bothersome. He lifted the cup and put it against his lips before he remembered it was empty, and made a displeased face into the cup, but it wasn't because of the tea…
"Would you put that book down for a second so I can make more tea?"
"Hmm?" The noise wasn't entirely a question, more an irritated inquiry as to why exactly he should be disturbed in the middle of a page, or in the middle of a book, more like, because he was halfway through and it would only take a couple more hours to finish, or maybe a bit longer, but it would take all night if he kept being interrupted like this. Oh, John knew that noise well enough, or at least, knew Sherlock well enough to know that was what it probably meant.
"Let go of me so I can make tea. Yours has gone cold and mine's been empty for nearly an hour." A pause, as his cheeks went a little red at the words that were coming out of his mouth. "Or you could put that book down and kiss me."
That got a reaction. Sherlock's chin rose from his shoulder. Granted not exactly the kind of reaction he'd been aiming for, as he twisted around. The detective's face was actually amused, which was a good sign, though. It was that little quirk at the corner of his lips that he got when John said something unexpected and amusing.
Even in private, it wasn't something that they spoke of. The quiet domesticity was usually enough. Just the two of them, and Mrs. Hudson. But every once in a while, when it was just the two of them, and they were sitting alone, and nobody else would ever hear them, that was the only time John ever said anything, and it was never much…
"So the choices are either put the book down and kiss you, or allow you to get up and go banging around in the kitchen, and then at some point you'll come back and I'll have to stop again so you can sit back down?"
"I could sit in the other chair."
Sherlock thought about that for a moment, then with a completely straight face, "But we're both comfortable sitting here, now."
John felt the smile tugging at his lips, and the distraction of his uncomfortable realization at just what he'd asked of Sherlock hit him, but he didn't have time to complete that train of thought before there were lips pressing against his, in that awkward, formulaic way that was also somehow comfortable and just so very Sherlock that he didn't particularly mind it.
The faint taste of the cream and sugar that Sherlock took in his tea still lingered on his lips, John noted in the back of his mind. And in a few moments, the kiss was over.
"There, I didn't even have to put down the book."
That twitch of his lips, then they were both laughing, and settled back into the chair, John content for now.