“Smile” is a horror film that sets up nearly everything — its highly effective creep factor, its well-executed if familiar shock tactics, its interlaced theme of trauma and suicide — before the opening credits. In an emergency psych ward, Dr. Rose Cotter (Sosie Bacon), a diligent and devoted therapist, is speaking to a woman who sounds like her soul went to hell and never made it back. Her name is Laura (Caitlin Stasey), and she describes, in tones that remain rational despite her tremulous panic, the visions she’s been seeing that no one else can.

She sees faces — or, rather, a spirit, a something, that reveals itself in people’s faces. She can feel it lurking; the spirit’s signature is a face that will stare back at her with an evil smile, a scary grin of the damned. Describing all this, Laura becomes so distraught that she starts to convulse. Then the doctor turns around, seeing a smashed flowerpot on the floor, and Laura has disappeared. But no! She’s there, with a pottery shard in hand. And now she’s the one smiling, as she digs the shard into her neck and scrapes it along, slitting her throat in blood-gushing slow motion. Put on a happy face!

The demons Laura was seeing didn’t die with her. That night, Rose goes home to her big chilly modernist house next to a woods, and after pouring herself a glass of wine and sitting in the semi-darkness, she sees the same thing that Laura saw. A face, shrouded in shadow. The more she looks at it, the more she can see that it’s grinning.

The smile, as a signifier of maniacal fear, goes back a long way. Just think of Jack-’o-lanterns and the Joker, or the leer that flashed across the mottled face of Linda Blair’s Regan MacNeil, or the rictus grins in a movie like “Insidious” or the movie that inspired it, the great 1962 low-budget freak-show classic “Carnival of Souls.” In “Smile,” the first-time writer-director Parker Finn, drawing on films like “Hereditary” and “It Follows” and “The Strangers,” turns the human smile into a spooky vector of the shadow world of evil. The movie has a shivery quality that I, for one, thought “Black Phone” lacked. Yet I wish “Smile” were more willing to be…suggestive.

Laura, the throat-slitter, had a trauma in her past: She watched a professor commit suicide right in front of her. And she committed suicide right in front of Rose. Do you sense a pattern here? The movie fills in that pattern, and once it does, and we get the hang of it, “Smile,” in form, turns into a rather standard thriller about uncovering the mystery of an ancient curse.

If you’re haunted by visions of people smiling at you, but no one else sees them, the world is going to think you’re crazy, and much of the drama in “Smile” revolves around Rose looking like a therapist who’s lost her mind. Sosie Bacon, who’s like a taut neurasthenic Geneviève Bujold, creates an impressive spectrum of anxiety, tugging the audience into her nightmare. It makes sense that Rose, teaming up with her police-officer ex-boyfriend (Kyle Gallner), turns herself into an investigator, because that’s what therapists are (at least the good ones). And she’s got a primal trauma of her own: the suicide of her mother, which we glimpse in the film’s opening moments. “Smile” lifts, from “Hereditary,” the idea that the emotional and psychological demons that are passed down through families are our own real-life ghosts. But in this case it’s a megaplex metaphor: literal, free of nuance, illustrated (at the climax) with a demon who sheds her skin, all the better to get inside yours.

There’s a good scene set at Rose’s nephew’s seventh birthday party, where the usual tuneless singing of “Happy Birthday” melts the film into a trance, and the kid unwraps a present that stops the party dead in its tracks. But I would have liked to see three more scenes this dramatic — especially in a movie that lasts 115 minutes. “Smile” will likely be a hit, because it’s a horror film that delivers without making you feel cheated. At 90 minutes, though, with less repetition, it might have been a more ingenious movie. (And why is “Lollipop,” the 1958 hit by the Chordettes, played over the closing credits? It’s one of my favorite songs, but it has zero connection to anything in the movie.) Yet let’s give “Smile” credit for taking a deep dive into the metaphysics of smile horror. The nature of a smile is that it draws you into a connection with the person who’s smiling. That’s why the forces who come after Rose are more than just bogeywomen. That’s why it feels like they’re meant for her.