In my opinion, the two scenes in Lord of the Flies that stand out as the most frightening are the scene in which Simon is killed and the scene in which the hunt is on for Ralph. These two scenes are the most disturbing and frightening to me because they both show how low the boys have sunk into their dark nature. Simon was an innocent member of the group, nearly an outsider to the boys, and he was killed for no reason. The description of the wild chanting, the dance, and the fire build up the suspense in the scene and foreshadow the dark event to come.
Similarly, when Ralph is chased by the boys at the end of the novel, the fire spreads around the brush, and so many elements come together to trap Ralph. It is frightening that the boys are so unreasonable that they are now out to get Ralph, and the description of the fire helps develop this tone.