The first time Mycroft saw his little brother make that most endearing of gestures, Sherlock was only a few months old. Much like his older brother, Sherlock had always been a quiet child, too busy thinking to speak. But unlike Mycroft, he would go from absolute silence for long periods to a torrent of babbling in the nonsensical language of babies, often without warning and at the most inopportune of moments, usually the middle of the night.

Mycroft was watching Sherlock and wondering if he, too, had looked so strange and inhuman. Sherlock was in one of his silent periods. Mycroft crossed his eyes and stuck out his tongue in an attempt to make his brother smile. When he uncrossed his eyes, though, he was greeted not with a smile, but with a cute tilt of the head and a sound that can only be expressed as a question mark.

When Sherlock was two, Mycroft was no stranger to the head tilt that signified that Sherlock was thinking deeply. He didn't tell anyone, but it was by far the favourite thing he watched his little brother do. Sherlock had been watching the cat chase a rolled up piece of paper, head gently tilted to his right, as if trying to analyze every little motion.

Mycroft smiled fondly. He could tell already that Sherlock would be his brain-friend, someone he could think with instead of just watch like the kids at school.

Mycroft was twelve. Sherlock was five. It was Christmas, and one of their cousins had set up a model train set. Sherlock was watching it intently with that funny little head tilt, and Mycroft knew he was trying to figure out how it worked.

As ever, when he was thinking, the younger Holmes was silent and still, except for shining, glittering eyes that defied all attempts at colour identification. The other cousins wanted to put their toys on the train, but Sherlock had always taken them off. He wasn't very good in the company of others, and, like Mycroft, much preferred the company of his mind.

"But why do there only have to be eight electrons in the outer shell?"

Sherlock was nine. Mycroft was practicing his chemistry class presentation on his younger brother, who was just as intelligent as (probably more than) the other people in Mycroft's class and thus would be an ideal first audience. For a moment, Mycroft was thrown off-guard. His own interest in chemistry wasn't terribly high, but he managed an answer nonetheless. Mycroft's soul glowed as he realized Sherlock's head was tilted.

Mycroft had come home from university for the summer. Sherlock, now fourteen, was watching a documentary on the behavior of bees, that ever-so-slight head tilt present, and it was clear he hadn't left the sofa for some time.

"It worries me when he gets like this," their mother said. "He refuses to eat. He's been watching about bees for a day and a half now."

"He's thinking, Mum. It's not that difficult to see. I'm sure he'll snap out of it or fall asleep, eventually."

Sherlock was seventeen and so absorbed in what he was doing, the tilt of his head was slightly more pronounced than usual. He was sitting in a lecture hall, attending a lecture on forensic sciences—a birthday gift from Mycroft, who was right there beside him (though not enjoying it too much). The other students' attentions were either divided between rapid note-taking or an expression of overwhelmed boredom. But not Sherlock. Sherlock didn't need to take notes—it was all in his head.

Mycroft hadn't seen him so engrossed in learning and thinking since the bee incident (which had continued for a total of two days and five hours, ending in Sherlock losing consciousness). It was nice to know that the thing Mycroft found most endearing about his younger brother seemed to continue into his early adulthood.

Mycroft watched Sherlock's head go from its normal vertical position into its now-familiar tilt. They hadn't talked much for years, rarely seen one another in person, and now that Sherlock had begun his investigative career in earnest, Mycroft had decided to maneuver him into a case he would find interesting.

It was remarkable, noted Mycroft, the things that give one away. Here Sherlock was, age twenty-seven, being told about the theft of an important piece of political paperwork which, if it fell into the wrong hands, would plunge the world into another world war, and he was pretending to not be interested. But of course he was, once the details were being revealed.

And the most adorable (though Mycroft hated the word, it was the only one applicable) thing was, Sherlock didn't even know he was doing that gentle tilt of his head.

It was raining. An appropriate atmosphere, considering the conversation he was going to have with John Watson. He hated these days. Lying was no alien thing to him, but Mycroft wished he didn't have to pretend his brother was dead. Every Thursday, he'd come around to Speedy's and have lunch with John. With Sherlock supposedly gone, he had to keep up the pretense that he had no one but John to turn to.

"Yes, we've been having some trouble at the Embassy," Mycroft began, trying to pretend that he was pretending not to hurt too much. But as he went into further detail—nothing too classified, of course—he noticed something.

John's head was tilted gently to the right.