Milk bubblegum

A famous one was for "The House at Haunted Hill" (also starring Vincent Price). At a pivotal scene in the movie, a skeleton with red glowing eyes would swoop out over the movie theater audience on a wire.

Now the Tingler had a much more unique concept.

The story of the Tingler is already insane. In the movie, Scientists discover that all human beings are born with a parasite in their spines called a "Tingler" that feed off of human fear. Called "The Tingler" for how you feel a rush run down your spine during extreme fear, which turns out to be the feeling of the parasite growing. Tinglers grow and will slowly curl in on themselves and will eventually crush the human spine it's wrapped around. Humans have evolved a natural defense mechanism, which is screaming when they get scared. Screaming weakens the growth of the Tingler, and prevents it from reaching a lethal size.

A scientist discovers this creature after a movie theater owner's wife, who was deaf and mute, died because she could not scream when frightened. Turns out he had murdered his wife by purposefully terrifying her, allowing the Tingler to grow to a lethal size.

So here's the gimmick. It's simply but ingeniously effective, as the entire movie was basically written to "sell" the gimmick.

William Castle had buzzers installed under the theater seats. This caused the seats to, at specific points in the movie, vibrate against the movie audience's backs.

There was also some live action sequences I'm just gonna copy paste from the wiki

During the climax of the film, The Tingler was unleashed in the movie theater, while the audience watched a climactic fight scene in Tol'able David (1921). The film stops and, in some real-life theaters, the house lights came on, a woman screamed and pretended to faint and was then taken away in a stretcher; all part of the show arranged by Castle.[12][8] From the screen, the voice of Price mentioned the fainted lady and asked the rest of the audience to remain seated. The film-within-a-film resumed and was interrupted again. The projected film appeared to break as the silhouette of the tingler moved across the projection beam. The image of the film went dark, all lights in the auditorium (except fire exit signs) went off, and Price's voice warned the audience, "Ladies and gentlemen, please do not panic. But scream! Scream for your lives! The tingler is loose in this theater!"[15] This cued the theater projectionist to activate the Percepto! buzzers, giving some audience members an unexpected jolt, followed by a highly visible physical reaction. The voices of scared patrons were heard from the screen, replaced by the voice of Price, who explained that the tingler was paralyzed and the danger was over. At this point, the film resumed its normal format, which was used for its epilogue.

There were also nurses stationed at the theater doors and planted "Screamers and fainters" who would be gurneyd out of the theater and "whisked off to hospital" past the audience, who would then come back and repeat the process for the next showing.

And that's the story of the movie "The Tingler".

I recommend looking up Willaim Castle and his movies further.

Also this is what a Tingler supposedly looks like

What everyone expected of me as an adult: "Actually, there's nothing unfair about it. I was just whining about something that was for my own good."