Well, perhaps the moment when Harold discovers the old diary in the attic. As he reads it, he realizes that the events described in it seem to be repeating themselves in his own life. The diary tells of a curse, and as he continues to read, strange things start to happen around him. For example, objects start to move on their own, and he feels a cold breeze even though all the windows are closed.
In Harold's story, the part where he gets lost in the dark forest at night is truly terrifying. He can hear strange noises all around him, like whispers and growls. There are also shadowy figures that seem to be following him. The darkness is so thick that he can barely see his own hands in front of his face, and every step he takes could lead him to an unknown danger.
Since I don't know the exact story, if it's about the forest scenario I mentioned earlier, the scariest part could be when Harold is all alone after Tommy goes missing. The silence, broken only by the occasional strange noise, and not knowing what took Tommy would be terrifying.
In my opinion, the scariest part in Harold's story when he was in the old mansion and the doors started slamming shut while he was trapped. It gives a sense of helplessness and the unknown that is really terrifying.
In some of the stories, the sudden appearance of the supernatural entities is the scariest part. Like in the haunted house story, when a ghostly figure just pops up in front of you out of nowhere. It gives you an instant shock.
Well, perhaps Harold has a story where a young girl finds a strange old doll in the attic. The doll seems to have a life of its own. It starts to appear in different places around the house, and every time it shows up, something bad happens. For example, the girl's pet suddenly gets sick when the doll is left near its bed.
For the nurse, the movement of the gurney by itself and the sheet on the corpse moving were the scariest. It goes against all logic and normalcy, especially in a morgue which is already a spooky place. It made her feel that there was something supernatural going on.
One of the scariest parts in 'It's Him' is the build - up. As the story progresses and more and more strange things happen that are associated with 'him', the tension mounts. For instance, if objects start moving on their own and the only explanation the characters can think of is 'it's him'. And when the final confrontation with 'him' is approaching but you still don't really know what 'him' is, that's extremely scary.
The invasion of privacy in smart home device hacks is very scary. Knowing that someone could be watching you through your own camera or messing with your home environment without your permission is a huge concern. It makes you feel vulnerable in your own home, which is supposed to be a safe place.
The sudden appearance of something strange. In the story of the face at the window, the babysitter is just going about her job, and then suddenly there's this creepy face. There's no warning, and it's something that seems out of place and threatening, which is really terrifying.
The feeling of helplessness. For example, in a haunted house story, when you're trapped inside and there's no way to escape the terrifying presence. You can't fight it because you don't know what it is. It makes the story really scary as hell.
The suddenness is often the scariest part. Lightning can strike without warning, like in the story of the hiker where it hit the tree near him so suddenly. Another scary aspect is the power it shows. When it causes destruction, like splitting a tree or hitting a chimney and causing sparks. It makes people realize how vulnerable they are.