The element of the supernatural can be very effective. For instance, 'I saw a shadow on the wall. It had no source of light.' This defies the normal rules of physics and makes the story spooky. And the use of common fears like the dark also works. 'I entered the dark cellar. I felt something touch my neck.' The darkness already makes people uneasy, and the added touch makes it scarier.
One element is the unexpected. For example, in 'I opened the fridge. A severed hand was inside.' The normal act of opening the fridge is suddenly made terrifying by the unexpected discovery. Another is the use of the unknown. In 'I heard a knock. No one was there when I opened the door.' The mystery of who or what knocked creates fear.
The use of the senses can be effective. In a story like 'I smelled a strange odor. Then I saw a shadow moving towards me.' The smell and the visual of the shadow create a scary atmosphere. Also, a sense of isolation helps. 'I was alone on the island. I heard a howl that didn't sound human.' The fact that the character is alone makes it scarier.
One effective one is 'I was home alone. Then I heard a voice whispering my name from the empty basement.' It gives an immediate sense of dread as being alone at home is a common situation and an unexplained voice is very creepy.
Suspense is a key element. For example, in a story where a character is alone in a dark house and hears a creaking noise, not knowing what's causing it right away builds suspense. Another element is the unknown. When the source of fear isn't clearly defined, like a shadowy figure that the protagonist can't quite make out, it's scarier. Also, a sense of isolation, such as a person being stranded in a remote place, makes the reader feel more vulnerable and thus makes the story scarier.
Effective extremely scary two - sentence horror stories often use the fear of the dark. 'I turned off the lights. In the pitch black, I felt something breathing on my neck.' Darkness is something that humans are instinctively afraid of. Also, the use of the abnormal. 'The mirror showed my reflection. But then, my reflection blinked when I didn't.' This abnormal behavior makes it scary. And the feeling of being watched. 'I sat in the empty park. I couldn't shake the feeling that someone was watching me from the bushes.'
One element is the element of surprise. For example, in a two - sentence story like 'I opened the attic door. A monster lurked behind it.', the sudden revelation of the monster is unexpected. It gives the reader no time to prepare, hitting them with fear right away.
One element is the unknown. For example, in a story where there is a strange noise at night but the source is not known right away. Another is the use of the dark. Dark places like closets or basements create an immediate sense of fear. Also, the use of creepy characters such as ghosts or monsters, like the haunted doll in some stories. These things combined can make a short kids scary story very effective.
One element is the sense of the unknown. In short scary cliffhanger stories, like when a character hears strange noises in a dark alley but doesn't know what's making them. Another is suddenness. For example, a character is walking calmly and then suddenly something grabs their foot. Also, the lack of resolution makes the reader's mind race with possibilities.
Surprise is a key element. For example, in a short story where a character seems to be in a safe situation, like sitting in their living room, and suddenly a hand reaches out from under the couch. It's unexpected and scares the reader. Another element is the unknown. When there are things that are not fully explained, like a strange noise in an empty attic that the character can't identify, it creates fear.
Surprise is key. For example, in a story, when a character thinks they are safe but then something unexpected like a sudden noise or a strange figure appears. It catches the listener off - guard.
They are effective because they are concise. They get straight to the point of scaring you.