As Sherlock hit the ground, he was beginning to realize that perhaps this was a very bad way to tell John he was alive.

The timing wasn't the best, of course, but it had been two years, and Sherlock didn't want to admit it, but he was excited to see John again. But belatedly, as John's hands throttled his neck, Sherlock was beginning to think John didn't quite feel the same.

Sherlock expected happiness, relief, joy, curiosity, anything really, but he didn't expect anger. And so much of it.

So when Mary asked him later if he understood human nature, he answered truthfully.

Because honestly, he didn't.

Because it wasn't just the once, it was three times that John hit him. (Once was an anomaly, twice was the start of a pattern, but three? Three meant something deeper.)

So Sherlock went back to 221B with a bloody nose, split lip, and a nagging sense of disappointment. For how smart he was (and sometimes he wondered) he never expected John to be so angry.