[caption id="attachment_146154" align="aligncenter" width="1280"] 'The Zygon Invasion' (Photo: BBC)[/caption]

Paranoia is at all all-time high, a rogue Zygon faction has decided to try and take over humanity and they're happy to use their shape-shifting power to full advantage. Meanwhile the Doctor is doing his best to prevent a world war, but his best friends and allies keep being replaced by his enemies.

In a situation like this, tiny details become very important. So here are 10 things, some trivial, some less so, that you may not have appreciated fully in the first view of this impossibly tense story, particularly if you watched bits of it through your fingers:

Judging by the way the Doctor plays "Amazing Grace" on his guitar, he's clearly a fan of Jimi Hendrix. Most specifically the feedback-drenched version of "The Star-Spangled Banner" Hendrix played at the 1969 Woodstock festival.

The Doctor introduces himself to Walsh, the UNIT commander whose squadron is so devastatingly fooled by the Zygons, as "Doctor Funkenstein," which is a reference to a single of the same name by the '70s funk group Parliament, taken from their 1973 album The Clones of Dr. Funkenstein. Her reply "Yes, we know who you are," is of course a nod to the reaction most people (and Daleks) gave whenever Harriet Jones MP introduced herself, from "Aliens Of London" to "The Stolen Earth."

The Doctor referring to people by nicknames taken from children's entertainment is clearly becoming a thing, although this time the Doctor has good reason to refer to Jemima and Claudette—the Zygon high command—as "Monster High" (named after a series of popular gothic fashion dolls made by Mattel) and "Cinderella," as they are carrying branded backpacks with those characters on them.

One of the interesting things about Z67, the anti-Zygon gas referred to by both Kate Stewart and Walsh, is that it appears to have been developed by a naval surgeon. Harry Sullivan, one of the Fourth Doctor's companions who was himself imitated by a Zygon in "Terror of the Zygons," was a doctor in the navy. And according to the Brigadier in "Mawdryn Undead," he ended up working on something "hush hush" at Porton Down, the very place that Kate claimed had developed the gas.

[caption id="attachment_146154" align="aligncenter" width="1280"] Harry Sullivan in 'The Terror of the Zygons' (Pic: BBC)[/caption]

Also, Kate Stewart refers to the events described in "Terror of the Zygons" as having occured "in the 70s, 80s." This isn't woolliness on her part. The various storylines involving UNIT are flatly contradictory over the dates in which they occur. UNIT is a key part of the 1970s adventures of the Third and Fourth Doctors, and these were set in what was then the near future (as is the case with the Second Doctor adventure "The Web of Fear," which was made in 1968 and set in 1975, when the future Brigadier Lethbridge Stewart was just a colonel). However, the 1983 Fifth Doctor story "Mawdryn Undead," which features two Brigadiers meeting across different points in his time stream, was set in 1983 and 1977, and yet in both cases the Brigadier was older and had retired in 1976 to teach at a public school. Consequently, whenever the Doctor's past in UNIT is referred to, it will always be dated in quite a vague fashion.

Recently writer Peter Harness tweeted this moment of unused dialogue between the Doctor and Osgood, proving that her romantic aspirations have only been affected by work, not her tendencies towards cosplay:

Discarded: DW: D'you have a partner? Boyfriend? Osgood: (shakes head) You kind of give up on dating if you have anything to do with UNIT.

— Peter Harness (@mrpeterharness) October 16, 2015

The term "poncing about," as used by the Doctor to explain why he enjoys traveling in the presidential plane, could do with a bit of definition. As a noun, ponce has been used as an insult—suggesting effeminacy or undue weakness—and as a verb it means either to borrow or take something that can't be given back, like a cigarette or a biscuit. Poncing about, by contrast, means to act in a daft or silly fashion—most commonly to pretend to be something you are not, for comic effect—or to deliberately give oneself airs and graces, just for the fun of it.

Osgood's question mark shirt (and the Doctor's question mark underpants) is a throwback to a fashion quirk that spans four Doctors. The Fourth, Fifth and Sixth Doctors all wore shirts with an embroidered question mark on them, and the Seventh had a knitted vest (known in the U.K. as a tank top, and modeled by one of the Osgoods at the beginning of the story) with question marks all over it, and a question mark handle on his umbrella. Why? Well that is the question.

Once again, the term hybrid is being bandied around, which refers back to the Time Lord prophecy mentioned by Davros in "The Magician's Apprentice." Currently the tally of possible hybrids—"two great warrior races forced together to create a warrior greater than either"—includes the Daleks infused with regeneration energy, Ashildr, Sam Swift and now Osgood.

The Twelfth Doctor remembers having "snogged a Zygon" (British slang for a fairly intense kiss). The shape-shifter in question had taken the form of Queen Elizabeth I in "The Day of the Doctor," and it was the Tenth Doctor she kissed.

10 Things You May Not Know About ‘The Zygon Inversion’

Now go back and read the entire 10 Things You May Not Know About Doctor Who archive.