- Any scene involving fanservice on a victim being attacked/eaten by "them". If not by "them".
- Particularly in the first episode where Toshimi is torn apart on the stairs, when her so-called "friend" abandoned her to die. You see closeups of "them" biting into her arms and legs as "they" drag her further into their midst, 'til all you see is the lower half of her body writhing in agony along with her pleas... which become anguished sobs, which stops once she starts gurgling on her own blood... and then... Damn, what a way to go.
- Picture being on a bus during the outbreak, when you suddenly realize that the other passengers are being Eaten Alive, including the driver - knowing you have nowhere to run... knowing you'll be next.
- Just about any scene exposing the darker nature of humanity.
- The first zombie that approaches Takashi and Rei opens his mouth a bit wider than a normal human mouth should open, showing More Teeth than the Osmond Family and some drool.
- Every single scene involving Shidou's "cult".
- Shidou himself is pretty horrifying from the start, but look at his "subjects". The first one we see (the one with the phone) is clearly on the last vestiges of sanity, and the others are essentially little more than wild eyed, slobbering sex slaves. Perhaps the worst part is that they were all once normal highschool students, but thanks to the depravity and megalomania of a single man...
- Made worse, considering he tried to manipulate Shizuka into staying with them when Saya decided it was best to split off from Shidou and his students. Given his obvious intentions for her, had Hirano not held him at gunpoint, Shizuka might've been gang raped.
- Then in chapter 29, you find out he's STILL ALIVE.
- Any scene that show's Kohta's darker side. He's been so traumatized by years of abuse during high school that he's not above killing the living people who made his life a living hell.
Nightmare Fuel / Highschool of the Dead
Of course, being a series about a Zombie Apocalypse, it was inevitable.