Horror films are designed to elicit fear and terror in viewers through plots involving evil supernatural forces that intrude into the everyday world. They deal with primal human fears like vulnerability, death, and the unknown. Horror films developed from folktales, myths, ghost stories, and melodrama. They often combine science fiction elements when the menace is related to technology or aliens, or involve supernatural powers controlling helpless victims. While some rely on graphic effects, well-made horror films can tap into human dreams and uncover the inner horrors and virtues of humanity.