Horror is a film genre seeking to elicit a negative emotional reaction from viewers by playing on the audience's primal fears. Inspired by literature from authors like Edgar Allan Poe, Bram Stoker, and Mary Shelley, horror films have existed for more than a century. The macabre and the supernatural are frequent themes, and may overlap with the fantasy, supernatural fiction and thriller genres. Horror films often deal with viewers' nightmares, fears, revulsions and terror of the unknown. Plots within the horror genre often involve the intrusion of an evil force, event, or personage into the everyday world. Prevalent elements include ghosts, extraterrestrials, vampires, werewolves, demons, gore, torture, vicious animals, evil witches, monsters, zombies, cannibals, psychopaths, and serial killers.