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Trivia: The Doctor's line about Sontarans perverting the course of human history is from the 4th Doctor's first spoken words when he wakes up from his regeneration in "Robot". The 4th Doctor in turn is referring back to the events of "The Time Warrior" and his first onscreen encounter with the Sontarans.
Trivia: The Doctor suggesting that they might be in a Miniscope refers to the original series episode "Carnival of Monsters". The Miniscope is a device that gathers people and objects from a narrow period of time and stores them, allowing viewers to watch the sequence of events and repeats them as they wish.
Trivia: The clockwork robots using spare parts to rebuild a spaceship, which the Doctor can't quite remember, is from "The Girl in the Fireplace" in series 2 of the new series.
Trivia: A dinosaur walking down the Thames, albeit with much worse special effects, was last seen in "Terror of the Zygons" episode 4.
Trivia: The Doctor's reference to a scarf goes back to his fourth incarnation, who wore that piece of apparel most of the time no matter what circumstances.
When Vastra runs to Jenny's body, Catrin Stewart's eyes are clearly moving beneath her eyelids.
Trivia: The Doctor's comment about a "gobby Australian" is a reference to Tegan Jovanka, an airplane hostess and his companion primarily during his fifth incarnation.
Trivia: The observatory from "Tooth and Claw" is seen in one of the TARDIS rooms.
Trivia: The Doctor uses a crystal from Metebelis Three. The crystals were last seen in the original series "The Planet of the Spiders" in 1974: the same year this episode takes place.
The submarine's depth gauge is labeled improperly; the dial lists the units as "METEPC", or the word "METERS" transliterated into Cyrillic characters, rather than translated into Russian. The Russian word for "meters" is "метров," or "metrov" when transliterated into Roman characters.
When the submarine surfaces, breaking the ice cover, the diving hydroplanes on the sail are in the horizontal position. All submarines with hydroplanes on the sail rotate it to the vertical position before breaking the ice cover. The edge of the hydroplanes are reinforced and angled for this purpose.
The bridge console shows high definition flat-screen plasma displays. In the early 1980s, the equipment used would be CRT displays.
When the sub is resting on the ridge at 700 meters (2300 feet) depth, the missiles can not be launched. The maximum launch depth for the Delta III/IV submarines are 55 meters (180 feet).
Trivia: The HADS (Hostile Action Defense System) is mentioned for the first time in the series since the 1968 serial "The Krotons."
Trivia: When Clara meets the girl from the bookcover, Summers Falls, the writer is Amelia Williams.
After Solomon teleports away with Nefertiti, a voice over plays saying "Hostile targeting in progress". A computer monitor is then shown which misspells it as "Hostile targeting in process."
Trivia: When Oswin tells the Doctor about the Intensive Care unit, she mentions that they are survivors of failed Dalek campaigns on the planets Spiridon, Kembel, Aridius, Vulcan, and Exxilon. This refers to events from the classic series' stories "Planet of the Daleks," "The Dalek Master Plan," "The Chase," "The Power of the Daleks," and "Death to the Daleks," respectively.
Just before the Doctor enters the TARDIS near the end of this episode, three children see him. When River is examining the files in the future, she has photographs of the children shown at the moment they met the Doctor but there were no cameras around to take those precise photos.
Trivia: This makes the first televised appearance of a Cybermat in thirty-six years. They were last seen on-screen in the 1975 serial "Revenge of the Cyberman." The Cybermat's appearance here is closer to its very first appearance in "The Tomb of the Cyberman," rather than the sleeker (and primarily CGI) design of "Revenge."
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Classics, Dark Comedy, British TV, Time Travel, Creatures