Trivia: The Doctor mentioning that someone tried to move the Earth once before, a long time ago, is a reference to the First Doctor serial "The Dalek Invasion of Earth", in which the Daleks intended to replace the planet's core with an engine in order to do the moving. And, of course, the Daleks are responsible for this episode's titular planet theft as well.
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.
Trivia: Filming of this episode was delayed for several reasons. One was that the school that they were filming in was discovered to have asbestos just after they started, so they needed to find a new place. And in the scene in and outside of the cafe, filming was delayed when several drunk people wandered onto the set and started messing everything up.
Trivia: Very few actors have played separate villains in three different Doctor Who shows. Julian Bleach plays Davros in the main Doctor Who series, the Ghostmaker in Torchwood, and the Nightmare Man in The Sarah Jane Adventures. Paul Marc Davies plays the Futurekind leader in Doctor Who, something in Torchwood (I forgot) and the Trickster in Sarah Jane. Nicholas Briggs also provides voices in all three series for aliens and robots.
Trivia: The 11th episode of series 2 was originally going to be a story written by Stephen Fry, set in the 1920s. However, most of the special effects budget for the episode wound up being used for "The Satan Pit", so Fry's episode was bumped to series 3. "Fear Her" was commissioned as a last-minute replacement, and with intentionally minimal special effects. Fry's episode wound up never happening because he didn't have the time to rewrite it with Martha as the companion instead of Rose.
Trivia: The episode takes place in late July/early August, but was actually shot in February. The Doctor's early line where he wonders what is making it so cold, as well as the Isolus pod's heat-sink abilities, were added to cover for why people's breath is visible in outside scenes.
Trivia: The events of the previous episode, "A Town Called Mercy", actually take place during the events of this episode, specifically at the end of the seven-week anniversary trip the Doctor takes Amy and Rory on. The evidence? In "A Town Called Mercy", the Doctor mentions Rory having left his cell phone charger in King Henry VIII's ensuite. During the montage showing the anniversary trip in this episode, the Doctor, Amy and Rory are shown hiding under a bed in the past, and a whispered conversation reveals they are hiding because Amy just accidentally married King Henry VIII.
Trivia: The scenes involving the football/soccer game were shot in the same park as the scenes from "Forest of the Dead" involving Donna meeting the virtual Miss Evangelista. The dead giveaway? The gazebo where Donna and Miss Evangelista talked is visible in the background of the first shot of the Doctor, Craig and Sophie arriving.
Trivia: Elton's line of "We've even got a bit of a love life" was controversially received as his lover Ursula was a head stuck in a paving slab, and the only kind of sex life they could have was oral sex. Russell T. Davies defended this, saying it was a harmless joke that children would not understand.
Trivia: Caecilius is played by Peter Capaldi, who later on took over the role of the Doctor from Matt Smith. It was later written into the storyline that the reason the Doctor's regeneration picked that face was as a reminder to himself that he saves lives. In addition, Karen Gillan, who later played Amy Pond, plays one of the Sybilline priestesses.
Trivia: A list of the Doctor's regenerations in the new series, by in-universe chronological order: Eighth Doctor (Paul McGann) - fatally injured by crash-landing on Karn during the Time War, and temporarily revived by the Sisterhood, who gave him a choice of what his next incarnation would be (50th anniversary mini-episode "The Night of the Doctor", released in 2013). The War Doctor (John Hurt) - regenerates of old age after the end of the Time War ("The Day of the Doctor", 50th anniversary special, 2013). Ninth Doctor (Christopher Eccleston) - absorbed the entire Time Vortex from his companion Rose ("The Parting of the Ways"). Tenth Doctor (David Tennant) - radiation poisoning from stepping into the broken Nuclear Bolt cabinet to save Wilfred Mott's life ("The End of Time"). Eleventh Doctor (Matt Smith) - old age, after spending nearly a thousand years on Trenzalore defending it from all of his archenemies, and his companion Clara managed to persuade the Time Lords to give him a new regeneration cycle ("The Time of the Doctor"). Twelfth Doctor (Peter Capaldi) - injuries sustained while fighting the Master and the Cybermen onboard a time-dilated Mondasian colony ship (Injuries sustained in "The Doctor Falls", regeneration occurred in "Twice Upon a Time").