John sighed as he stitched up Sherlock's forearm. The cut wasn't too bad, but it was deep enough to need several stitches.
"Really, Sherlock, you've got to be more careful," he chided. "We're both lucky to have escaped with only a few cuts and bruises." John had been right behind Sherlock as they chased the fleeing suspect, but of course Sherlock had caught up to him first, and the man had managed to get in one good swipe with his knife before John had knocked it out of his hand. The suspect had put up a fight, actually landing a punch to John's left eye before John had tackled him and pinned him to the ground. John could still feel the sting of the man's right hook, and knew he was probably already developing what would be a quite impressive black eye.
As John finished with Sherlock's arm, he realized the detective had been rather quiet during the process. This was not something John was used to, as Sherlock usually complained and whined constantly while being doctored. John worried that he might be in shock.
He finished, then looked up at Sherlock. "Please try to take it easy, you don't want to tear these stitches," was what he was going to say, until he got a good look at Sherlock's face and the words died in his throat. Sherlock was staring at him, eyes wide with wonder, and appeared to be studying his face quite intensely. It made John feel uncomfortably like a dead body in a morgue, and he started to protest, but there was something else, some other expression on Sherlock's face John wasn't sure he had ever seen there before.
They both sat there for a few more moments, Sherlock looking at John as though he was a particularly interesting corpse, John trying to identify the look on Sherlock's face.
At first when Sherlock raised his hand, John flinched a bit. The hand stopped for a moment, then continued moving, until it brushed, ever so faintly, across John's developing bruise. John realized that must be why Sherlock was studying him so intently, although he had no idea what was so fascinating about a black eye. Sherlock's lips parted ever so slightly, and he inhaled audibly.
John blinked stupidly in surprise. He wanted to ask Sherlock what the hell he was playing at, but something about the way his flatmate was looking at him stopped him. He still couldn't name the look on Sherlock's face, but it didn't feel like Sherlock's usual cold indifference, so he kept still.
Sherlock's hand went up to John's face again. This time he lingered, delicately tracing the outline of the bruise with his graceful fingers, then ever so gently placing his fingers at the corner of John's eye, where it hurt the most. Sherlock's cool fingers felt soothing, and John closed his eyes. Sherlock swiped his thumb softly over John's eyelid, and exhaled slowly, audibly.
John opened his eyes and smiled at Sherlock. John knew that he often surprised Sherlock, and also that this was not a thing Sherlock was used to. He's seen the way the detective studied him, and though John was no genius, he was also not an idiot. Sherlock loved cataloging information about John, and although John knew this, he never let on that he knew.
Of course Sherlock was fascinated by John's injury. It was new information. Sherlock treated all new information the same, except information about John. He knew now what the look on his impossible friend's face was.
It was reverence.