Trivia: Freema Agyeman, who later played Martha Jones, plays Adeola in this episode. Russell T Davies later said that by the time he came on set and saw her performance, she had already shot her death scene - if she hadn't, he would have rewritten the episode so that she survived to become the next companion. Hence why Martha references her cousin Adeola in "Smith and Jones."
Trivia: The original plan for the episode was that the Doctor and Rose would both (in-universe, obviously) fake Scottish accents, and both drop them when things started getting interesting, leading to the locals realizing that they weren't who they claimed to be. The discovery that Billie Piper could not do a Scottish accent to save her life changed that quite quickly, although she did get to demonstrate her bad accent on-screen when Rose attempts to do one, and is swiftly told by an appalled-sounding Doctor to stop. As a final note, the Scottish accent that the Doctor puts on isn't actually David Tennant's real accent - it's a different Scottish accent.
Trivia: When Elton and Ursula come back after their "storming out" because Ursula forgot her phone, if you look closely, the headline on the newspaper Victor is reading says "Saxon leads in polls" - a sneaky reference to the villain of the next season, Harold Saxon... Better known as the Master.
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: 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: 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.