“This woman had a horrible relationship with her Mum,” says Collette. “Terrible! No nurturing whatsoever. And actually her whole life has been manipulated by this woman; it’s a total betrayal.”

Without entering into spoiler territory, Ellen’s demise isn’t the only death Annie will face as a supernatural secret lurking in her family history is unveiled. Yet the story is a slow-burn, taking its time before a terrifying crescendo.

“When I started to read it – I’ve been told it’s a horror film – I was like, ‘Where is the scary stuff?’,” the actress adds. “This felt like a classic family drama, so it was really surprising to read and that alone made me want to do it, let alone the fact that I get to go for it.”

No question, Collette does “go for it” in a film that takes the Australian star to extremes she’s never come close to in her 25 years on screen. “It was kind of amazing being allowed to do that,” she says.

“There’s so much resentment and rage in this woman. And she really doesn’t understand where [this has come from] … until horrible things happen in the movie. But before that, her entire life, she’s had this unsettled knowledge that something is wrong. There’s this ominous feeling hanging over her.”

Married to Steve (Gabriel Byrne), Annie is the mother of 16-year-old Peter (Alex Wolff) and 13-year-old Charlie (Milly Shapiro), two increasingly disturbed children. As the story unfolds, it becomes clear just how fractured her family history is.

“It’s not in the script but Ari came up with the idea that she married her therapist,” says Collette. “Gabriel’s character used to be her therapist. So there’s this notion that she needs taking care of and she’s vulnerable.”

Aster was keen on casting Collette. “I’ve loved her work ever since Muriel’s Wedding,” he says, referring to P.J. Hogan’s 1994 comedy that made Collette a star.

“It occurred to me that I had never really seen her chew apart the scenery in the same way that this film demands. We know what she’s capable of … but I’m not sure if I had seen her go this far.” Collette didn’t balk at taking on the role. “To her credit, she knew how demanding the role was and she didn’t flinch.”

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While Collette is no stranger to supernatural movies – she was Oscar-nominated for The Sixth Sense, and followed it with the more tongue-in-cheek Krampers and the remake of Fright Night – she’s no horror junkie. “I’m too fertile already in my mind! I just don’t need those images,” she cries.

Nor does she view Hereditary as a traditional scary movie. “To me, it was just this really beautiful, painful, honest look at grief and how family dynamics change when you’re going through something that intense.”

After studying film at the AFI Conservatory and making several shorts, Aster wrote nine scripts before Hereditary. “It was a strategic move at that point to write a horror movie because I thought it would be easier to get financed. And it was an instinct that was validated.”

But this is no bloody B movie; rather it emanates from a personal place, hints Aster. “The film taps into different fears and preys on different fears and my fears are more existential. Rather than what’s hiding under my bed, it’s more what’s hiding in my genes.”

While Aster calls himself “a neurotic” and “a hypochondriac”, it’s something he channelled into his characters. When it came to pitching it, he had two ways of explaining it. “One is very simple – it’s a movie about a family that goes to hell. I think that’s totally apt.

“The other way I have been describing it, since I was trying to find financing, is that it’s a family tragedy that curdles into a nightmare in the way I think life can feel like a nightmare when things fall apart and disaster strikes.”

Jewish-raised, the New York-born Aster has never been to a seance – a communal contacting of the dead, which features heavily in the film – but he did a lot of research into spiritualism and the occult.

While the film operates as a serious drama, he says, “it’s also unabashedly a horror movie” that plays with the tropes of the genre. None more so than in the seance scene. “I was very aware that this is something that’s in every horror movie that’s about any sort of division between one plane and another.”

Already the film has recouped eight times its US$10 million budget, making it one of the indie hits of the year. “I didn’t know if this was something that would be rejected by most of the audience and embraced by a very small few,” admits Aster, who benefited from some canny marketing from US distributor A24.

At one screening, the company outfitted 20 viewers with Apple watches to track their heart rates. Graphs released showed spikes that saw some audience members’ hearts hit up to 164 beats per minute (considerably more than the usual 60-80 bpm).

When it came to constructing the film, Aster made it “a mission” to do everything as practically as possible, shooting in-camera rather than using computer-generated effects. He also kept tight control over the production, building Annie and Steve’s entire house on a sound stage.

“Everything interior was built from scratch,” he says. Every shot was also listed in advance. Collette remembers: “When I met with Ari, it was very evident that he was all over it. I’ve never worked with somebody so specific and meticulously prepared.”

Since the success of Hereditary, Aster has been preparing his sophomore feature, this time featuring British actress Florence Pugh, who won critical acclaim for her recent role in the film Lady Macbeth . The plot details are under wraps, but if it’s anywhere near Hereditary then we’re in for a breathless ride.

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Whether its drawing gothic-themed pictures as a kid or watching Carrie, “I’ve always had a taste for the macabre,” he says. And that’s putting it mildly.

Hereditary opens on September 6

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