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Nightmare Fuel: Neverwhere
This exchange cements the fact that Croup and Vandemar decidedly aren't human.
Croup: If you cut us, do we not bleed? Vandemar: ...No.
Only on the first read. After you see how very literal-minded Vandemar is, it's clear he's saying that yes, they do bleed, or rather, that they don't not bleed. That said, they definitely aren't human, and nearly every scene with them in it contains at least a bit of Nightmare fuel
The duo's habit of eating everything alive. Rats, cats, humans, basically anything with a pulse. At one point, Vandemar finds a sandwich and instead of eating it, uses it as bait to catch pigeons and eat them whole.
The whole of Richard's Ordeal, but especially the train carriage full of rotting corpses, every single one a suicide.
The idea of being permanently invisible to everyone around you. You can't withdraw money, your fiancee of 18 months doesn't recognise you, your desk at work's been removed, you can't hail taxis, your house gets sold while you're still living in it...
Whereever Anaesthesia went on Knightsbridge.
Mr Croup gleefully eating an object he had doted on with apparent love and affection mere seconds before is so horrifying it borders on Nausea Fuel.
The Big Bad the Angel Islington is extremely unnerving as a being so utterly self-obsessed and self-righteous it's gone well past the point of insanity.
Where the fuck is Ingress? Yes, she's probably pretty darn Genre Savvy if her sister is anything to go by, but she's still a little girl. Croup and Vandemar murdered her mother right in front of her as well as the rest of her family(I doubt she knows Door's alive) and kidnapped her, and stashed her somewhere. And she hasn't gotten the hang of her opening skills because otherwise Islington wouldn't need Door alive That poor kid is probably going to be SO friggen traumatized by the time Door rescues her. If she can even be rescued... Considering what Croup and Vandemar tend to do with loose ends, after Islington says she "isn't going to work" well.... *shivers*