Doctor Who

When Vastra runs to Jenny's body, Catrin Stewart's eyes are clearly moving beneath her eyelids.

Trivia: The Cybermen's weaknesses to gold and cleaning fluid are mentioned. Their gold weakness was first mentioned in "Revenge of the Cybermen," while their weakness to cleaning fluid (more accurately, solvents such as acetone and nail polish remover) was in "The Moonbase."

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."

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."

During the teaser, the policewoman opens door 214, walks forward down the hall and opens door 215, and then continues forward down the hall and opens 214 again.

Trivia: Among the photographs on the hotel's walls are a Sontaran, a Silurian, a Tritovore, a Hoix, a Catkind, and a Judoon.

Trivia: The Doctor mentions that the minotaur-like creature is similar to the Nimon, a race of aliens that featured in the Fourth Doctor serial "The Horns of Nimon."

Future Amy says she learned the trick of making the hand-bots touch each other to stun them on her first day in the facility, when in fact she had already been there a week before she learned to do it (in the first room).

In this episode Mels comments "You said guns didn't work in this place! You said we're in a state of temporal grace!". This is a reference to a plot device from the original series in which weapons could not be discharged within the TARDIS. This was first mentioned in "The Hand of Fear (3)." In later episodes this plot device was abandoned such as "Earthshock."

Hitler shoots Mels, but at no point do we see blood (which Rory refers to) or even a hole in her dress.

Rose Tyler, Martha Jones, and Donna Noble all make an appearance as holographic images as the Doctor was selecting a voice interface.