In Conan Doyle's A Scandal in Bohemia, Sherlock asks Watson how many steps lead up to their quarters at 221b Baker Street. Watson hasn't a clue. "I know there are 17 steps, because I have both seen and observed," Holmes tells him. Because Sherlock fans are similarly observant, there are 17 steps leading to the first floor of the Sherlock Holmes Museum, and another 17 between the hall and front room on the Cardiff set of Sherlock.
6. Matt Smith wanted to be Watson
A week before landing the part of Doctor Who, Matt Smith auditioned to play John Watson; Steven Moffat decided he was "too barmy", and that one Sherlock was enough. Martin Freeman, on the other hand, arrived at his audition having had his wallet stolen on the way and was in such a bad mood it was assumed he wasn't interested. The following week, he returned in a better frame of mind, read with Benedict Cumberbatch, and the part was his.
7. Benedict Cumberbatch hates Sherlock's hair
The actor's preparations for looking the part of Sherlock include intense Bikram yoga sessions, swimming, and no smoking or drinking during filming. But there's one thing he especially hates doing: growing his hair. As he told The Times, "I can't think of a wittier or even accurate comparison, but I just think it makes me look a bit like… a woman."
8. But he may be autistic
Late 2013, autism charity the National Autistic Society cited Sherlock's single-mindedness, inability to understand social norms such as sarcasm, and incredible feats of recall as evidence that he might be autistic. This, despite Watson making a direct reference to his friend's Asperger's in The Hounds of Baskerville.
9. Mark Gatiss learnt to swim in Moriarty's pool
At the end of season one, Moriarty lures Holmes and Watson to a beautiful public pool in order to kill them. The location used is Bristol South Swimming Pool; according to the Sherlockology blog, this is also where a young Mark Gatiss learnt to swim.
10. Sherlock and Mrs Hudson knew each other in a previous life