Spare and Efficient
Nothing is the book version of one of those modern, architecture-magazine homes that's all hard white edges and stainless steel. By the end, you're just looking for a couch and an afghan, and maybe a cat and a cup of hot chocolate for good measure.
Janne Teller doesn't waste words. She's not trying to make you feel cozy. Instead, Teller uses only as many words as she needs to convey the relevant information. She's, in a word, terse. There's a lot of why-use-a-sentence-when-a-fragment-will-do writing, which is true to the age and emotional maturity level of our narrator: a 7th grader isn't going to talk like Faulkner, or it wouldn't be realistic.
And in telling us only as much as we need to know, Teller leaves a lot to our imaginations. We fill in the blanks of the gruesomeness, and it becomes even scarier that way. It's the same idea as the horror movie that doesn't show you the monster until the very end: instead, the director focuses on building suspense, knowing that there's nothing she could show you that's as scary as what you could imagine.
Sofie's rape, for example, is a very short chapter. There's a ton of buildup, like when Agnes says, "It was a dreadful day at school" (13.8). Once again, that's the only sentence on the whole page, but she follows that with a description of the day and their interaction with Pierre Anthon that afternoon.
The actual rape, however, is never shown. We don't go with Sofie to the sawmill that night. All we get is Agnes's take on it the next day: "there was just a smidgen of blood and some slime on a checked handkerchief lying at the top of the heap of meaning, and Sofie was walking a bit funny, like it hurt when she moved her legs." The reader is left to imagine the gruesome details, and people can imagine some pretty gruesome stuff.