One very scary horror story is about a haunted house. People who enter it start to see apparitions of a family that was brutally murdered there long ago. They hear the screams of the victims and feel cold hands touching them in the dark.
They leave a lot to the imagination. Consider 'The empty swing moved by itself.' It doesn't explain why, and that's what makes it so terrifying. Your mind fills in the blanks with all kinds of horrible possibilities, and that's the power of very very short horror stories.
I don't really know about kmjs horror stories specifically, so I can't say for sure if they are very scary. It depends on a person's tolerance for horror.
One very horror story is about a haunted house. A family moved in and every night they heard strange noises, like scratching on the walls. Objects would move on their own. In the end, they discovered the house was built on an old cemetery.
A group of hikers got lost in a forest. As night fell, they noticed strange markings on the trees. They then heard howls that didn't sound like any normal animal. They started to feel like they were being hunted. One by one, they disappeared until only one hiker was left, running for his life, not knowing what was chasing them.
One horror story could be about a Santa who turns out to be a serial killer. He uses the Santa disguise to get close to his victims. Another might involve a haunted Santa suit that drives the wearer insane. And perhaps there's a story where Santa is in a post - apocalyptic world and is no longer a symbol of joy but of terror.
The element of the unknown. When we don't know what's lurking in the shadows or what's going to happen next, it scares us. For example, in a story where a character hears strange noises but doesn't know the source.