The unpredictability of their behavior. Spiders can move quickly and quietly. In some scary stories, a spider might be lurking in a corner and then suddenly jump or crawl onto someone without any warning. Also, the idea that some spiders are venomous adds to the fear. People are afraid of being bitten and suffering from the effects of the venom, like in stories where a character gets bitten by a mysterious spider and then falls ill or has strange symptoms.
The most frightening aspect is the unexpectedness. A spider on your cheek is not something you anticipate. It's a violation of your personal space in a very creepy way. For example, if you're just sitting quietly and suddenly feel something crawling on your face, it gives you an instant jolt of fear.
Another scary element is the strange noises. Like in some stories, there are unexplained growls or whispers during the Skype call which make the situation very spooky. It makes you feel like there's something evil lurking. Well, it could also be some sort of technical issue that creates these sounds, but in the context of a scary story, it adds to the horror. For instance, a person was having a quiet call and then suddenly there was a loud screeching noise that seemed to come from nowhere. It really startled them.
The unknown nature of the spider's venom makes it scary. We don't know how it will affect us.
The unknown. You might encounter strange cultures, rituals, or superstitions that you don't understand. I heard a story where a traveler unknowingly entered a place where there was a local superstition about not wearing a certain color. He wore that color and all the locals stared at him in a really creepy way. It made him feel very unwelcome and scared.
Isolation also plays a role. When characters are alone, like in a big, old, deserted house, they are more vulnerable. It makes the reader feel that there's no one to help them. A good example is in 'The Shining' where the family is isolated in the hotel in the mountains. And the use of the supernatural, like ghosts, vampires or demons, scares people because it defies the laws of nature that we are used to.
The use of the senses. Scary stories often play on our senses. They might describe a strange smell in a haunted place, or a cold touch that can't be explained. For example, in a story about a haunted hospital, the smell of old medicine and the cold drafts that seem to come from nowhere all contribute to the overall scariness of the story. It makes the story more immersive and terrifying.
The sense of the unknown is a big factor. In scary leprechaun stories, they often have their own hidden world that we don't fully understand. They can be mischievous and unpredictable. They might lead someone astray in the woods, or play tricks on people that have serious consequences. And the fact that they are often associated with lonely and desolate places, like old ruins or deep in the woods, gives an overall feeling of unease.
The long teeth themselves are a major frightening element. Just the sight of a creature baring its long, sharp teeth can send shivers down your spine. It gives an immediate sense of danger.
The loss of humanity in zombies. They used to be normal people but are now mindless, flesh - eating monsters. It makes us think about how fragile our humanity is. Also, the sense of isolation. When the world is overrun by zombies, the survivors are often alone or in small groups, cut off from the rest of the world. This loneliness adds to the fear.