Sherlock frowned, his lips parting as if he was going to reply, but instead he closed them, thinning, and frowned deeper.

He had thought it incredibly obvious, and of little consequence, and he would have said so - but he knew that look that John was giving him, and for a moment it actually caused him to shut up.

Well.

For a second, anyway.

"It isn't my opinion," he said instead, a low complaint like a child might make when they felt they were being punished unfairly. But he didn't make a point beyond that.