- Acting for Two: Katy Manning provided the noises of the chickens seen in episode one herself.
- Cast the Runner-Up: Both Cheryl Hall and Jenny McCracken were earlier considered for Jo Grant. According to the DVD Commentary for the Special Edition of the story, they were on the final shortlist of six actresses seen for the role. Barry Letts promised both actresses he'd use them in the future after Katy Manning was cast.
- Ian Marter's casting as Lt. Andrews was a case of this as well — he was the favored pick to play Capt. Mike Yates, but had to refuse as he already had other commitments he couldn't get out of.
- Creator's Favorite Episode: Barry Letts named this as his favourite of Robert Holmes' contributions for the show. He particuarly felt that the Drashigs were one of the best monsters in the series.
- Development Gag: Who would want to see the Cybermen? A reference to the fact that Terrance Dicks didn't like them at all.
- Recast as a Regular: Ian Marter (Lt. Andrews) would later play the Fourth Doctor's companion Harry Sullivan.
- Similarly Named Works: The title is the same as a Ray Bradbury short story "Carnival of Monsters" published in the 1940s. In it, a millionaire on Mars lures several health officials into his house. They meet a variety of gruesome fates inspired by different horror writers. However, the title of this episode may be unrelated.
- Working Title: The Labyrinth and Peep Show.
- Writer Revolt: It's hard not to see a certain undercurrent of Biting-the-Hand Humor to the story, in which the Doctor and his companion get trapped in a tiny universe made up of corridors and generic monsters to run away from down those corridors. An eccentrically-dressed intellectual gentleman and his plucky blond assistant are involved, but only because they've figured out that scaring children gets them paid. All of this goes on under the purview of privilege-obsessed literal grey-faced bureaucrats who complain about monsters and view entertainment as purposeless. Robert Holmes was asked to do a Strictly Formula story, and instead did a Deconstructive Parody.
- You Look Familiar: Michael Wisher makes another appearance, this time as Kalik.
Trivia / Doctor Who S10 E2 "Carnival of Monsters"