In order to cater to modern social trends and broadcasting regulations, Sherlock gave up smoking pipes and switched to nicotine patches.

There's a scene in Episode 2 - The Blind Banker - where Watson throws a pen to Sherlock, and Benedict Cumberbatch caught it successfully the first time during filming (he usedHe used a mirror to see where the pen flew), but the movement was so fast that the cameraman didn't catch it.

At the end of Episode 3, Moriarty lured Sherlock and Peanut to a public swimming pool in an attempt to kill them. The swimming pool that appeared here was the South Bristol Swimming Pool, and this swimming pool was none other than Mark Gatiss.The place where I learned to swim as a child.

The three episodes of the season were filmed in the exact opposite order as they were broadcast.