They had been at it for what felt like days, but in reality John knew it had only been hours. His vision was beginning to blur, his hand cramping.

He hated paperwork.

By the looks of it, the other two men crowded into Lestrade's office were similarly unimpressed with the sheer volume of forms and reports they were being required to fill out in triplicate for the official police records. Sherlock, as he always did after the end of a case, looked exhausted despite having slept for nearly ten hours, and appeared to be keeping himself awake through sheer determination and stubbornness alone.

As much as he could be a nightmare to work with though, John knew that Lestrade appreciated Sherlock's dedication to correct procedure after a case was closed, even if it meant in filling in extra forms because of Sherlock's unique working relationship with the police service.

As such, the post-case paperwork slog was quickly becoming alarmingly familiar to John. With the criminal caught the trio would go their separate ways to their beds, sleep for a ridiculously long time, and then meet back in Lestrade's office the following day to tackle the endless reports and evidence forms before the details began to slip away from them.

They worked in companionable silence, only broken by the slurping of teas (or coffee in Sherlock's case when he was feeling especially run down) and the scratching of pens, oblivious to the outside world.

John shifted, trying to stretch his back which was already aching terribly when Sherlock's fingers cramped and slipped. The young detective let out a curse, (John had discovered that Sherlock rarely cursed, but when he did he was always tired), shaking his hand out and apparently giving it up as a lost cause because to John's surprise his simply swapped the pen to his left hand and carried on.

So, Sherlock was ambidextrous. Surprising, perhaps, but not unexpected. They had been caught in many a situation where the ability to use his left hand as flexibly as his right would have helped John massively in escaping various situations, being able to pick locks with both hands was a skill he was still learning. So really, Sherlock's ability to do so shouldn't have come as such a shock because it only made sense in his chosen career that Sherlock applied the same focus to his escapology as he did to his deductions.

No, what was surprising, John grasped after a moment, was something he had unconsciously observed himself.

Medical training or no, it was immediately clear from Sherlock's posture, and the speed and fluidity of his writing, that he actually preferred writing this way. Therefore, John deduced, (and oh grief he was starting to pick up Sherlock's terminology), Sherlock was naturally left-handed.

Why then, did he always pick up the pen with his right? There was no way that Sherlock would do it to 'fit in', he hardly cared about being different in everything else, why would this matter? Unless, John realised, he had been taught to do so from a young age and it had become a long engrained habit.

"John?" Sherlock's questioning voice drew him out of his thoughts and to his embarrassment John noticed that both Sherlock and Lestrade had stopped working and were giving him a worried look. He also noticed that he had probably been staring at his flatmate for the last few minutes.

"Yeah, sorry," John shook his head to clear his thoughts, "just noticed something odd."

"Odd?" This time it was Lestrade that spoke up. Beside him, Sherlock frowned.

"It's nothing important," John replied trying to turn his attention back to the forms.

"It was clearly enough to distract you from these admittedly dull forms for several minutes," Sherlock observed simply, "please do share, if only to distract us from the boredom." Lestrade smirked at the comment.

"It's just," John hesitated before deciding to power through, "it's just that you're left-handed. I'd never noticed before."

Sherlock's mouth formed a small 'oh' as his eyes flitted between the pen held loosely in his left hand and John.

"Only," John continued after a pause, "you always use your right. I was trying to work out why and must have spaced out for a bit."

Slowly, carefully, Sherlock laid the pen down.

"No one's ever noticed before," he muttered quietly as he slowly flexed the fingers of his left hand, "how could you tell?" His inquisitive gaze met John's, he didn't look upset, just intrigued.

"Your posture," John replied as his brain caught up with the conversation, "you relaxed unconsciously, and your writing was faster and smoother than usual."

"Hmm," Sherlock's mouth quirked up, "I'm impressed John, it seems as though you're picking up some deductive abilities of your own." It seemed that for Sherlock at least that was the end of the conversation because he picked up the pen again and was about to go back to scrawling the details of the case when John blurted out.

"I couldn't work out why though." Sherlock froze, frowned again, put the pen back down.

"Sorry?" Lestrade, who had at this moment been content to observe the discussion in silence, quietly filing away this new knowledge of his younger colleague, suddenly spoke up.

"Why do you insist on using your right hand to write when it's clear you aren't comfortable doing so?" John aimed his question at Sherlock, who seemed to have been caught off-guard by it.

"Left-handedness was not encouraged at school," Sherlock finally murmured, his gaze resting firmly on his hand at the pen.

"Not encouraged?" John prompted and finally Sherlock looked up at him, eyes unreadable.

"No," Sherlock's voice remained quiet, almost timid, "it tended to smudge the ink." The detective fell silent, his body language was screaming for them to stop questioning.

"Did they force you to switch hands?" Lestrade asked, his voice had also softened to the tone he often used with victims. Sherlock recognised it immediately and took offence.

"I wasn't abused inspector," he spat, "if that's what you're getting at."

"I didn't suggest that you were." Lestrade shot back calmly, a concerned frown on his face.

"I just… struggled to comprehend emotional intent, facial expressions, vocal intonation, body language at that age," Sherlock admitted, a blush rising on his cheeks, "they didn't mean for me to change if it was uncomfortable, I see that now, they just wanted to help me ensure I presented my work well. I misread the situation, observed that of my twenty-four classmates I was the only one writing with my left hand and made a deduction. So no, Lestrade, I wasn't abused, I just misunderstood."

Sherlock's voice trailed off, his eyes once again fixed on the table in front of him. Suddenly John recognised that they had also misread the situation. Sherlock hadn't closed up because he was afraid, but because he was ashamed, embarrassed even, to admit a weakness, a mistake.

"You were just a child Sherlock," John said softly, seeing the detective beginning to clam up in the ensuing silence, "you don't need to keep doing it, you know, not if it's more comfortable to write left-handed, we're not going to judge you and you don't need to be embarrassed, you're allowed to make mistakes, no one's perfect."

"You are." The words slipped out and hung heavily between them as Sherlock realised he had spoken aloud. "Sorry, ignore me, no idea why I said that. So, forms?"

John saw through Sherlock's attempt at distraction for what it was.

"No, it's fine," he said softly. Sherlock paused.

"It is?" Sherlock sounded confused and hopeful at the same time.

"Yes, it is, good even," John replied calmly, watching at Sherlock attempted to process the words.

"Really?" Sherlock asked tentatively.

"Really," John confirmed before turning back to the long-forgotten paperwork. Lestrade thankfully took his signal and did the same, allowing Sherlock time to absorb the words.

They finished the paperwork quickly and quietly, as though nothing had happened, as though Sherlock hadn't had an emotional revelation and they didn't bring it up again, not even when they next sat down together after a case and Sherlock unconsciously picked up the pen in his left hand, clicked it on, and started writing.

But over the table, John and Lestrade both spotted, glanced at each other, and smiled.