Most of the things in film that scare me aren't visual, they're plot-related scenarios that the clips don't make sense without the context of actually watching the movie up to that point, so I'll just write a short list, I'll try to explain why it's scary without spoilers if I can.
In The Mouth Of Madness (1994)
- Even though The Thing (1982) is probably the most scary movie ever made because it's the most plausible horror movie ever made, watching In The Mouth Of Madness at night after a couple rough days of insomnia is an experience that will surely drive you insane on an immersive level.
The Fourth Kind (2009)
- I only watched this movie because I've got an old friend who said it was the scariest movie he's ever seen while he was on acid. So naturally, I took 2 hits of LSD, and then watched it. He's right. It's probably the most insane trip I've ever had.
- There's no way to avoid the spoiler for this one, unfortunately. So this is a warning. If you don't want to spoil the movie, than read no further. But first a little backstory. Much of what makes the film scary is implied, rather than shown. There's definitely some disturbing and gnarly scenes in the movie, but the implication of the anthesis is what's scary. See, back in 2014, when Interstellar came out as a movie, Interstellar implied the idea that if a black hole is large enough humans wouldn't spaghettify after the redshift. What's implied in Interstellar is that light particles are the Information of Hawking Radiation on a Black Hole wherein the light particles beyond the event horizon is that imprinted Information on the Black Hole. What Annihilation (2018) implies is that if such a thing is hypothetically possible at a macrocosmic scale, than if we can pass through one for wormhole theory as implied in Interstellar, than potentially a 4th dimensional extraterrestrial could pass through it into our 3 dimensional existence were it to condense its form to be that of light particles. shaped into humanoid form So the implied theory of Interstellar is followed up by the counterpoint of the implied theory of Annihilation, which is that if a 4th dimensional extraterrestrial entered into 3 dimensional existence it would be through the formality of light particles since light particles have the least amount of mass and the highest concentration of energy, allowing it to shift and transform, mirroring and inversing mathematical and molecular structures of organisms within an area of effect to create a tesseract, or a 4D cube inside a 3D space, similarly to how Virtual Box software works. Basically, it creates a place for it to exist in the between, like a bubble of sorts. However from within the tesseract, the 4D space would seem as 3D space. And from the outside of the tesseract, from the 3D space, it would appear as a strange barrier of sorts due to dimensional perceptual differences and how light and light particles function in 3D space. It's just that, it's implied in the writing of the movie, but never formally stated.