If you thought the new trailer for The Nun was enough to keep you up at night, the film Hereditary Is guaranteed to give you the fear.

And that's a scientific fact.

You could ask any ten people what the scariest film is they've ever seen, and chances are you'll get ten completely different films rhymed off.

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You'll be faced with a list of films that chances made sure you had trouble sleeping - but the 2018 Studio A24 movie starring Toni Collette is said to even give the Exorcist a run for its money.

Credit: A24

The company behind Hereditary, which shows Collette uncovering a terrifying supernatural family secret, kitted out a random selection of film-goers with Apple Watches to monitor their reactions during the horror film.

The watches tracked the heart rates of the viewers as the film's horrific events unfolded on screen, in an attempt to get evidence of just how scary the film really is.

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What they found was very interesting - their heart rates raised to an alarming 164 bpm, compared to a healthy resting heart rate which is between 60 and 80 beats per minute.

Credit: A24

The company also published a graph - featuring five of the 20 participants' heart rate changes - and SPOILER: it seems to get super scary after the 90-minute mark.

Ok, it's not the most perfect science, but it does show that Hereditary is a really scary film.

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While it was in cinemas back in June, the film terrified audiences. One film fan tweeted: "It is an emotional and terrifying torture experience, an exquisitely slow burn blood-curdling performance.

"To everyone else there, sorry - the shrill shriek at the back of the cinema was me."

The film, which also stars Gabriel Byrne, Alex Wolff and Milly Shapiro, had a theatrical run-time of two hours and seven minutes, but the DVD/Blu-ray Director's Cut will include nine scenes that were deleted before Hereditary hit cinemas.

Credit: A24

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So if you couldn't quite manage to sit through the full film in the cinema without putting your hands over your eyes or making one too many trips to the toilet, it may not be the wisest move to go exploring those special features.