Mark Gatiss is an Internet Troll
Mark Gatiss, the co-writer and co-creator of Sherlock (along with Steve Moffat) is very fan-savvy. One of his favorite hobbies is using his twitter feed to troll fans by offering them tantalizing bits of information about filming Sherlock that actually may mean absolutely nothing. Moffat has been known to do this as well, but to a much lesser extent. Perhaps the most interesting one, and the most overlapping with the exposition of the “fourth wall” is this image:
which refers to a well-known Sherlock fandom blogger. This is supposedly a picture of Martin Freeman, and it may very well be, but I personally suspect that it could in fact be Gatiss himself hiding behind the parka hood. It really is John Watson’s parka from the series, but the hands don’t really look like Freeman’s. Compare:
There could be a number of contributing factors, but given that we already know how much Gatiss likes to mess with people, it seems entirely believable that he would do such a thing.
He also posted this picture during the filming of series 2, knowing that fans would see “bed” and immediately jump to sexy, sexy conclusions, which he purposefully did not bother to correct:
Further Gatiss tweets to follow.
Breaking the Fourth Wall (They Know About the Porn)
The phrase “breaking the fourth wall” is used among theatrical types to refer to the imaginary “fourth wall” that separates the actors from the audience. In the case of theater, the edge of the stage generally represents the literal “fourth wall,” and in the case of television, the screen obviously is what separates the action from the audience. To “break the fourth wall” is to do something that causes the actors and audience to acknowledge one another. This can be done either by the audience or by the actors, but usually consists of addressing the audience directly in one way or another.
Regarding the Sherlock fandom, it means that the cast and crew of Sherlock are aware of and somewhat involved with the fandom. Of course, any actors are aware of their fans in general, but the cast and crew of Sherlock have, on multiple occasions, gone out of their way to make fandom-specific references for the benefit of Sherlockians. The first incidence of this came to light in summer of 2011, when a photo surfaced of what is apparently Martin Freeman holding a sign that reads “Te quiero Jan y Rosalia xxx,” (I love Jan and Rosalia), who run a blog about Martin Freeman.
My apologies for the demotivational reframe, this is apparently the default mode of this photo now. Since the photo, there have been multiple troll posts on Tumblr, most notably from Mark Gatiss, good-humoredly acknowledging the insanity of the fandom.