How's this for kicks: at the end of "Day 3", Jack explains that in 1965, he handed over twelve orphaned children to the 456; when asked why, he says the exact same thing: "As a gift." He says it casually. With a shrug.
The sheer look of horror on the faces of Gwen, Ianto and Rhys as he says this.
The children were handed over to be used as drugs. It would almost have been easier if they were killed off.
This exchange:
The 456: "We have answered your question. You have one day to select and deliver the ten percent."
Frobisher: "And if we refuse?."
The 456: "We will wipe out your entire species."
The video of Gwen at the start of Day 5.
"Sometimes the Doctor must look at this planet and turn away in shame." That and the COMPUTER-GENERATED CROWD OF CHILDREN.
And later in that episode, the situation that's occurring in when she makes it. The British forces rounding up terrified children with their parents screaming and crying and desperately trying to get their children back. If that's not enough, knowing the Fate Worse than Death set to befall the kids... Probably the darkest moment in the Doctor Who universe as a whole.
This is a very powerful series of episodes, and the real Nightmare Fuel was not the 456, or even the fate of the children, but the actions of the ordinary humans in the governments of the world, the rationalizations and the plots and the cold ruthlessness. The world might have been better off with Harold Saxon.
They were using school league tables to decide which children should suffer a Fate Worse than Death. Exempting their own children, of course. After all, how could they be expected to make decisions if they're suffering from grief and trauma? The parents are told that the children are being sent for vaccinations; the government plans to pretend to have been duped by the aliens. And then one of the government people was ordered to hand his own daughters over. Knowing what would happen. He killed himself, his wife and children rather than do it. The whole thing was so much scarier than any alien, because this could happen. In a situation like this, it's all too easy to see decisions like this being made, for real.
The video of the children in the 456 cage.
This description of the scene from the TARDIS Data Core: "The child's eyes widen in shock, possibly at seeing another human for the first time since the 1960s." How is that not freaky?
The worst is the horrible joking about how the child (who turns out to be Steven) will "fry" by the guy monitoring the transmissions—and the mother's horrified realization of what they are about to do.
During the scene when the 456 are being affected by the deadly signal, transmitted by Steven, you hear the sound of a man screaming. It's either coming from Steven, or the 456, or the children connected to the 456, or all three of them at the same time.
Last but not least, during the 456's (possible) death scene, blood splatters the tank that houses the 456. It's either from the 456 itself or the children inside.
The end of Episode 4 is filled with this.
Notably there's the 456 choosing to "disconnect" with Clem, leaving him to effectively suffer a brain hemorrhage in Gwen's arms.
Also, when the 456 choose to gas the Thames House, we're treated to the sight of several people trying to bust out through the front doors in vain.
The scene in which the politicians discuss which children will be sent to the 456. It's not nightmarish like much of this miniseries, but this scene is definitely among the most unsettling television ever produced.
