It somehow seems to have become part of my head canon that Sherlock doesn't like metaphors. I had the same theme in The Adventure of the Illustrious Idiot (http://marysutherland.livejournal.com/17195.html), which contains the cracky twin version of this Sherlock. In both of the fics I'm fascinated by the possibility of Sherlock as pulling away from John precisely because he doesn't want to become the more caring man that John is imperceptibly making him into.