They’re not mother and son, but they talk like it. “He’s got a brain the size of a planet when you listen to him,” Lynne Ramsay says of Ezra Miller, the young co-star of her movie, We Need to Talk About Kevin. “Lynne showed me something interesting. The best direction a director can ever give to an actor is, ‘I trust you,’ ” Miller says of Ramsay.

They’re sitting in a hotel room – Ramsay, 41, the Scottish director of such art-house favourites as Morvern Cal-lar, and Miller, the 18-year-old American known for roles as the difficult son in movies like Another Happy Day and City Island – continuing what sounds like a long-running conversation. Ramsay is in a chair and Miller is beside her on the bed, holding a feather and wearing a string of beads around his neck.

He talks about being an “empty vessel,” and she giggles fondly: not a mother and a son, maybe, but a woman indulging a favourite child, and a teen-ager, perhaps showing off a bit for a parent figure.

What brought them together, though, is anything but maternal: We Need to Talk About Kevin is a dire drama about a woman named Eva (Tilda Swinton) who gives birth to a difficult child and grows to see him as a kind of monster. Based on a bestselling novel by Lionel Shriver, the story depicts a twisted boy (played by Miller as a teenager) who knows how to manipulate his father (John C. Reilly) and reveals his evil side only to his mother. Or – in a chilling subtext – perhaps Eva is simply suffering through a different kind of hell: She’s a woman who doesn’t love her child.

“It was something that hadn’t been spoken about, and I think it’s something that’s true,” Ramsay says. “A mother is meant to feel these instant emotions and instant connections, and I don’t think everyone does.”

Miller, who turned 19 a few days after the interview at last fall’s Toronto International Film Festival, says he related to the reality of the role, if not the specifics.

“Kevin is just … when I read the script, it was real … My attraction to the script was in the very simple thing of finding a real character.”

He wasn’t alone. Ramsay and her husband, Rory Stewart Kinnear, worked for four years on the script, paring a 400-page book down to an 87-page screenplay, as raising money became more and more difficult. But although it was a hard sell to financiers, it attracted a lot of interest among actors.

“It’s amazing how many boys did relate to it, you know, the (number) of people who wanted the part,” Ramsay says.

I suggest it’s a very juicy role. “It’s nothing but juice,” Miller says. “There’s not even a container. It’s just juice all over the place.”

Some critics see Kevin as a “demon seed,” but Miller says, “If there’s one ambiguity that I feel comfortable clearing up, it’s that I never for a second was thinking about how to portray someone innately evil.”