The new opening credits that were introduced in this episode were based on a fan-made YouTube video by Billy Hanshaw. Steven Moffat was so impressed by the video, he got in touch with Hanshaw to get it recreated by BBC Wales Graphics.
During the read-through of the script for this episode, the cast and crew-members filled the room with laughter when Peter Capaldi reached the lines ridiculing his eyebrows. The read-through was also the first time that Capaldi and Jenna Coleman had worked together, as Capaldi had been secretly auditioned.
When the newly regenerated Doctor is confused by the English accents of everyone in the room, Madame Vastra adopts a subtle Scottish accent (to reflect the new Doctor's Scottish accent). Neve McIntosh plays Madame Vastra with an refined English accent but is from Paisley, Scotland.
This is the longest normal episode.
At one point The Doctor asks a pedestrian, "Have you seen this face before?" and then continues to go into a rampant speech about never knowing where his face comes from. This is a reference to the fact that Peter Capaldi's face has been on the show well before he became The Doctor. In The Fires of Pompeii (2008), Capaldi played Caecilius, who met the Tenth Doctor. He also played John Frobisher throughout the third season of the Doctor-less Who spinoff Torchwood (2006).