Well, it's about the unexpected. In a 'two sentence horror story' like 'I heard a knock at the door. When I opened it, there was nothing but darkness.' The suddenness and the unknown in just two sentences can send shivers down your spine.
The brevity. With just two sentences, they leave a lot to the imagination. For example, 'I saw a figure in the fog. It disappeared when I blinked.' It's the quick jump from a normal sight to something unexplainable that makes it spooky.
In '4 sentence horror stories', the brevity is key. With just four sentences, they can quickly set a spooky mood. For example, by introducing a strange or menacing element right away, like a dark figure in the first sentence. Then, in the second sentence, adding an unusual or disturbing sound or action. The third sentence can build on the mystery, and the final sentence often leaves the reader with a sense of dread or unease. It's all about using concise language to maximum effect.
Another really scary one could be 'My phone rang at 3 am. The caller ID said it was me.' It plays on the idea of the self being something other or unknown, and calls at that time are always spooky.