Trivia: The Testimony are revealed to be connected to the University of New Earth, based on the planet of the same name seen in "New Earth" and "Gridlock." It's probable that Professor Clay, the Testimony's leader, died in the Bliss Plague from the latter episode.
Trivia: Clara's cameo was originally intended to be slightly longer, with her appearing on screen with the Doctor, Bill and Nardole. The three Companions were going to ask the Doctor which one of them was his favourite, and he was going to evade the question. Clara's brief, vision-like appearance came about because Jenna Coleman was too busy working on Victoria to shoot that version of the scene. She shot the scene in an office in London, with the background CGI-ed in.