In the 1980s, movies were pretty straightforward. There were rules and expectations: Actors should be beautiful, special effects realistic, endings clear and satisfying. It was a formula that hadn’t changed much since the dawn of movies themselves.

Then came “Blue Velvet.”

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Released 30 years ago in the fall of 1986, David Lynch’s groundbreaking thriller upended the rules of moviemaking so audaciously, so violently, that it polarized critics and reportedly caused walkouts in theaters. Why was its dialogue so strange, its symbolism so hokey, its actors rendered so grotesque? As for its impossibly happy ending — was this a joke? The film’s star, Isabella Rossellini, may answer some of these questions when she speaks at two local screenings of the film in the coming days.

Named for a shivery Bobby Vinton ballad from 1963, “Blue Velvet” takes place in a bizarro-version of small-town America. A rosy-cheeked Kyle MacLachlan plays Jeffrey, a naive youngster torn between a wholesome blonde, Sandy (Laura Dern), and a sexually decadent brunette, Dorothy (Rossellini, who lives in Bellport). In that sense, “Blue Velvet” was a classic noir, but the addition of a drug-huffing psychopath named Frank Booth (Dennis Hopper in a career-defining performance) turned the movie into a surrealist nightmare. Lynch’s scenes of sexual masochism and creative sadism were more than some moviegoers could handle.

Many critics praised “Blue Velvet” as a masterpiece, while others felt that its outrageous scenes — notably, an effeminate Dean Stockwell lip-syncing to Roy Orbison’s “In Dreams” — were gratuitously weird. Roger Ebert strongly objected to Lynch’s treatment of Rossellini, who in one scene wanders across a suburban lawn naked and dazed. “The more painfully a director violates the sensibilities of his audience and his performers, the more serious his intention should be,” Ebert wrote. He called the movie “an immature satire.”

In the years after “Blue Velvet” came a flood of films marked by camp humor (John Waters’ mainstream hits “Hairspray” and “Cry Baby”), ironic detachment (nearly everything by the Coen brothers) or shocking violence (“Pulp Fiction,” “Natural Born Killers”). For a while, at least, it seemed that the movies would never be straightforward again.