"The Zygon Invasion" features a lovely scene where a team of UNIT soldiers go to confront a group of Zygons in an abandoned church. And what follows is an intense standoff between the soldiers and the Zygons impersonating innocent hostages and their loved ones. The soldiers are manipulated by them and then led to their deaths. It just goes to show how effective and efficient the Zygons are at manipulation and killing.
"The Zygon Inversion" features the scene when Bonnie (who's pretty chilling in her own right) forcibly reverts a Zygon to his true form. The gradual, sporadic transformation is eerily reminiscent of Lampwick turning into a donkey in Pinocchio.
Bonnie makes the mistake of implying the Doctor doesn't understand the situation she's in:
Doctor, utterly enraged:"I don't understand? Are you kidding? Me? Of course I understand. I mean, do you call this a war, this funny little thing? This is not a war! (begins screaming)I fought in a bigger war than you will ever know! I did worse things than you could ever imagine! And when I close my eyes... I hear more screams than anyone could ever be able to count! (switches back to just talking) And you know what you do with all that pain? Shall I tell you where you put it? You hold it tight, till it burns your hand! And you say this: No one else will ever have to live like this! No one else will ever have to feel this pain! Not on my watch!"
Finding out that the Morpheus pods can hijack those who frequent them with an electronic signal that Rassmussen himself created. Even those who have used it once are in danger. "You've got something in your eye."
The Morpheus pods themselves can count on their own as well. They're named after the god of sleep and dreams, and they essentially take that away. It's a twisted moniker to name something after a god that was renowned for giving actual sleep and dreams, versus the machine that can simply rewrite your brain's chemistry and electrical stimuli from achieving proper sleep after only a few minutes, just so you can work longer than what should be natural for humans.
And then, of course, there's the ending. Holy shit, the ending. As the Doctor and Clara depart in the TARDIS, the Doctor convinced that he's missing something about this whole situation, we cut back one last time to Rassmussen's Framing Device, and we find out that the recording- ostensibly being used as an alibi to cover up his own involvement in the incident that destroyed the station- is in fact far more than that:
The chronolock. It appears on your neck in such a way that you can never see it, and you constantly have to ask others how long you have left to live. Everyone else can see it, and they judge you for your crime, and lastly there is what happens when it hits zero.
You begin your day with an exhilarating adventure with your love, about whose safety and survival you've been increasingly worried about. The two of you are asked for help by a young father and after some investigation you easily deduce the origin of the problem. You also realize early on that it's a con game. Easy, peasy. Unknown to you, however, said love has gone rogue and decided to take the chronolock upon herself as strategy to keep the young father safe. You discover this too late, and there is nothing you can do but hug her, receive some words of encouragement from her ... and then watch her die, screaming in agony before being teleported god knows where without time to so much as grieve. Not a very good way to end your day. (The Doctor, incidentally, directly identifies Clara's death as one of his nightmares in the following episode, "Heaven Sent".)
As explained under the "Doctor" folder, the Doctor's anger at Ashildr for indirectly being responsible for Clara's impending death. It's seldom a good thing when the Doctor gets angry at any other moment, but when he starts to threaten to bring UNIT and even the Daleks to the Trap Street to utterly annihilate everyone there — who are for the most part innocent refugees — as well as Ashildr, who didn't even intend for Clara to die and is screaming that he's "no longer the Doctor" and that no one's ever "stopped him" before, you know he's pissed off! Thankfully, Clara is able to eventually talk him down...
As asked in the Headscratchers Folder: Why doesn't the Doctor take revenge on Ashildr when it's clear he wants too? Simple. He can come back for her whenever he wants, but this is his only chance to find out who put her up to it. So he goes to find them himself, knowing that Ashildr will be looking over her shoulder for him for the rest of her existence, wondering if he's coming for her. He doesn't have to take revenge on her... because her fear of him possibly doing so is enough - she'll never have another night of peace again, because he could be waiting for her in every room, behind every door, anywhere and any when.
"Heaven Sent": The Doctor dragging himself, bleeding, up the stairs, while narrating about how long it take for Time Lords to die properly as every cell in their body tries and fails to regenerate.
