- The Cast Showoff: Word of God says that the "Humans are indomitable" speech was to show off the then-newly cast Tom Baker's speaking ability both in terms of his ability to pull off the kind of soliloquies that his predecessor would never have been able to, and in terms of showing off his gorgeous voice, with which the production team was universally infatuated. Some writers (especially Robert Holmes) would even sneak Inherently Funny Words into the Doctor's dialogue in scripts, just for the joy of hearing Baker say them.
- Creator's Favourite Episode: Tom Baker has stated that, of all the stories he'd filmed, this was his favourite.
- Deleted Scene:
- There was originally a scene where, in the final stages of larval infestation, Noah's head splits open and cracks in a torrent of acidic goo, that was cut because it was too graphic. There are conflicting reports on if the scene was ever filmed, and if it was, the scene was lost. (Probably for the best.)
- A scene was filmed where Noah confronts Vira and begs her to kill him to end his agony, which Philip Hinchcliffe decided to cut as it was too dark. The scene in the aired episode cuts from a shot of the Doctor looking on to a shot of him glowering and looking harrowed from a similar angle in a different room, with the door shut and no indication how they got away from Noah. Kenton Moore, who played Noah, expressed his opinion that he was furious about the scene going because it was crucial to the whole story. The missing scene is lost.
- Executive Meddling:
- In the original script, the Wirrn were simply ejected from the Ark in the shuttle. However, the BBC feared that the possibility of them surviving would frighten younger viewers, forcing Robert Holmes to kill them off at the end.
- This serial would have been a 6-parter, but it was split into a 4-parter with a 2-part sequel afterwards to avoid dragging out the story, which had been a recurring issue of the Jon Pertwee era. The 4-part format became a lot more popular with the classic series after this change proved to be successful, although 6-part stories would continue to be produced all the way though to Tom Baker's penultimate season (if one includes the unfinished "Shada").
- Missing Episode: The infamous deleted scene where Noah begs Vira to kill him rather than allow him to be turned into the Wirrn. The scene was filmed, but cut due to being too dark (despite being fairly crucial to the plot and explaining why Vira and the Doctor are so pale and distraught in the following scene).
- Shoot the Money: The characters spend an awful long time in the cryonic chamber (even though the useful controls, supplies and computers are elsewhere in other rooms) because the set was extremely beautiful and expensive and one of the most ambitious sets the series had yet executed. All scenes that don't absolutely have to take place somewhere else in the ship take place in it.
- Technology Marches On: The entirety of human knowledge on a space station built in the 30th century is stored on microfilm. Although Fridge Logic, storing the information on a solid state format that does not require power to operate ensures the data isn't lost by a computer failure over the long ages until awakening. It can also be read (at a pinch) with a torch and a magnifying glass and so doesn't require precious power needed for other duties like say... keeping the humans alive.
- What Could Have Been:
- The original script concerned a massive space ark carrying cryogenically-frozen humans, which has been invaded by the Delc. The Delc are fungi, grown from spores floating in space. The primary Delc take the form of floating heads, while their servitors appear as headless bodies. The Delc are impervious to most harm because any impact just causes the release of more spores. Fortunately, the Doctor eventually discovers that the Delc are susceptible to electrocution, and ultimately knocks the primary Delc out into space with a golf club.
- Vira was supposed to be black and possibly Haitian.
Trivia / Doctor Who S12 E2 "The Ark in Space"