The Tingler (1959)

Synopsis
As famous for the gimmick with which the film was shown as for its genuinely spine-tingling story, The Tingler follows a pathologist (Vincent Price) as he searches for the cause of a series of deaths and discovers that the victims have a large insect-like creature growing on their spinal chords. The creature attacks when the people are frightened and is only killed when the host emits a blood-curdling primal scream. This is coupled with a subplot to scare the deaf-mute owner of a silent movie house to death. Along the way, a couple of characters are injected with LSD and begin hallucinating like mad. When one of the nasty monsters "escaped" into a movie theater, the film's gimmick would begin. In order to further frighten audiences, director William Castle had certain theater seats rigged with small Army surplus devices that would deliver a mild electric shock to the spine in hopes of inducing terrified screams. Castle also planted audience members who would scream and faint. The house lights would go up, the film would stop and ushers would carry the unconscious person out of the theater. ~ Perry Seibert, All Movie Guide