The Tingler (1959)

In 50s B-film director and impresario schlockmeister William Castle's classic horror film:

• Castle's own introduction in the film's prologue with this word of advice: "I am William Castle, the director of the motion picture you are about to see. I feel obligated to warn you that some of the sensations, some of the physical reactions which the actors on the screen will feel, will also be experienced for the first time in motion picture history, by certain members of this audience. I say 'certain members' because some people are more sensitive to these mysterious electronic impulses than others. These, uh, unfortunate, sensitive people will at times feel a strange, tingling sensation. Others will feel it less strongly. Don't be alarmed - you can protect yourself. At any time you are conscious of a tingling sensation, you may obtain immediate relief by screaming. Don't be embarrassed about opening your mouth and letting rip with all you've got, because the person in the seat right next to you will probably be screaming too. And remember this - a scream at the right time may save your life."
• Castle's speech was followed by zoomed-in examples of disembodied screaming heads - three in all
• the character of mad, part-time pathologist/scientist Dr. Warren Chapin (Vincent Price) who made the discovery that the tingling sensation one felt running up and down one's spine when afraid was actually a "living" parasite that grew and lived in the vertebrae. When one couldn't scream or when one experienced prolonged scary situations (without having the therapeutic release of a primal scream), the parasite could grow to enormous size and cripple a person: "We know that it exists...We know that fear alone energizes it, gives it strength...The Tingler exists in every living human being and it's extremely powerful...Fear causes the Tingler to spread along the spinal column. And probably with those arm-like things between the vertebrae forces it to become arched and rigid...Screaming seems to stop the Tingler from bending the spinal column. Screaming may even dissolve it, or if it's a living organism, kill it...We now know that at the peak of terror, the Tingler is a solid mass, extending from the coccyx to the cervicals. If someone could stand the intense pain without screaming or otherwise releasing their tension until they die, I think that an autopsy would give us a Tingler that we could work with."

• Dr. Chapin's autopsy scene of deaf-mute patient Mrs. Martha Higgins (Judith Evelyn), the wife of silent movie theatre owner Oliver Higgins (Philip Coolidge); when he extracted the squirming, lobster-like centipede from her body, for a brief moment, it attached itself to his arm; and as he napped on the couch, the Tingler also crawled onto his chest and threatened to choke him; it released itself when his socialite wife Isabel Stevens Chapin (Patricia Cutts) returned home and screamed! Dr. Chapin surmised that if he returned the Tingler to Martha's body, it would die: "The Tingler exists in every human being, we now know. Look at that Tingler, Dave. It's an ugly and dangerous thing. Ugly because it's the creation of man's fear, which is ugly too. Dangerous because, because a frightened man is dangerous. We can't destroy it because we've removed it from its natural place...Fear made that Tingler grow from microscopic size to this. We can only hope when it goes back where it came from, it will also go back to a thing infinitely small - even die, because it's creator is dead and all fear gone."
• later in the film's climax, Dr. Chapin planned to place the Tingler back into Martha's corpse, but of course, the boxed creature escaped and entered a crowded film theater showing the silent film Tol'able David (1921); after scaring one young female by climbing up her leg, the Tingler crawled into the inattentive projectionist's booth; in pitch black, Chapin tried to calm the theatre audience with an announcement: "There's no cause for alarm. A young lady has fainted. She is being attended to by a doctor and is quite alright. So please remain seated. The movie will begin again right away"
• on screen, the projected film broke as the silhouette of the Tingler moved across the projection beam; the film theater went pitch black; the film audience (within the film and watching the film) were encouraged to scream to lessen the effects of tingling fear during a long black-out section by the voice of Dr. Chapin: "Ladies and gentlemen, please do not panic. But scream! Scream for your lives! The Tingler is loose in this theater! (Screams)..."

[Note: To enhance the effect when the Tingler was on the loose in the theatre, seats were rigged with vibrating devices to produce the tingling effect - a gimmick nicknamed Percepto.]

• after making another reassuring announcement, "The Tingler has been paralyzed by your screaming. There's no more danger. We will now resume the showing of the movie," Chapin rushed to the projection booth where the projectionist was being strangled by The Tingler; his screams caused the creature to drop to the floor, where it was captured in a film canister.
• in the film's conclusion, Higgins received the same fate as his wife, who had the Tingler reinserted into her spine by Dr. Chapin to neutralize its effects; the resurrected Martha caused her husband to die of fright - with muted screams. Dr. Chapin's words (in darkness) ended the film: "Ladies and gentlemen, just a word of warning. If any of you are not convinced that you have a Tingler of your own, the next time you are frightened in the dark, don't scream."