"Marble Hornets" is a movie of sorts, consisting of dozens of short films posted to youtube. "Marble Hornets" is an example of what is known as the found footage genre, perhaps most famously pioneered 20 years ago with The Blair Witch Project. "Marble Hornets" supposedly consists of a series of video cassettes that someone found.
I should explain something important: I wasn't able to get through Marble Hornets. It is a horror story, and it was frightening enough that I stopped watching and had about a week of what amounted to mental illness issues afterwards. It might have been where I was in my life at the time, but there was something about Marble Hornets that really fucked with me. Rewinding back a bit: Marble Hornets is supposedly the story of a man who searches through a disappeared friend's belongings. His friend was a film student making a typical film student movie, called "Marble Hornets", and the tapes were apparently the footage for this movie. But when his friend starts searching the footage, he finds something else entirely: the intrusion of a mysterious figure known as the Slender Man. The intrusion starts working its way into his life, as well...
All of that might sound a bit confusing, or maybe cliched, and people might wonder why this managed to be the scariest thing I have ever watched. Especially since some videos are just a man walking around in a park, two or three minutes of blurry black and white pictures, and then nothing. As far as I can figure, the reason this scared me so much, the reason I spent a week afraid of what was on the other side of the door, was that the videos use a lot of static, distortion, and other audio and visual anomalies. The viewer is not merely an audience, safely parsing data, but is struck by stumili that unexpectedly jump out at them. The success of the horror is in making the barrier between reality and fantasy paper thin, something that is done through alternation of the media itself. At least, that is my theory on it, but like I said, I wasn't able to finish. Someone with a stronger tolerance should go watch this and report back.