Horror films aim to scare and thrill audiences through the use of common themes like revenge, hauntings, demons, serial killers, religion, ghosts, and gore. Two frequently used themes are revenge and possession, as seen in films like Scream, Psycho, Halloween, The Exorcist, The Conjuring, and The Possession. Themes are at the core of horror and center around strange and frightening events that explore the dark side of life.