One: 'The mirror showed my reflection, but when I blinked, it didn't.' Another: 'I heard a knock at the door. When I opened it, no one was there, but the doorknob was cold as ice.'
These stories create a strong sense of horror in two sentences by leaving a lot to the imagination. Take 'The doll on the shelf had its eyes closed. Now it's staring at me.' It gives you just enough information to be scared but not so much that it over - explains. The reader's mind fills in the gaps with all sorts of terrifying possibilities. It's like a quick jolt to the senses, and our minds are wired to fear the unknown, so these short stories can be very effective at inducing horror.
The brevity. With just two sentences, they create a sense of mystery and unease quickly. For example, 'I woke up with a hand on my shoulder. When I looked, there was no one there.' It gives just enough to make your imagination run wild.
One 'two sentance horror story' could be 'I always sleep with a nightlight. Last night, I woke up to find it was still on, but I was in complete darkness.' It's terrifying because the contradiction between the nightlight being on yet in complete darkness creates a sense of the unknown and a break in the expected reality.
One could be 'I entered the abandoned asylum. A cold hand grabbed my ankle.' Another is 'She thought she was alone. But the eyes in the mirror said otherwise.' These short horror stories create a sense of dread quickly with just two sentences.
The brevity of '2 sentance horror story' is key. It leaves a lot to the imagination. For instance, 'I opened the attic door. A strange smell and a soft whisper greeted me.' The lack of details makes our minds fill in the blanks with the scariest things we can think of. Also, they can end on a cliffhanger, making the horror linger in our minds.
A man was walking alone in the forest. The moon was full but the trees were too thick to let much light in. He heard rustling behind him. He started to run. But then he realized the rustling was all around him, closing in.
One key element is the element of surprise. For example, 'I opened the fridge. A hand grabbed my wrist.' The first sentence sets a normal scene, and the second one throws in a sudden, unexpected and terrifying event.