Olivia Munn was "shaken to her core" when watching footage of a real-life exorcism.
The actress stars in new movie Deliver Us from Evil, which is based on a non-fiction book called Beware the Night. It follows a New York policeman who starts investigating a series of crimes, before joining up with a priest to try to stop things getting even worse.
Before the shoot Olivia and her co-star Eric Bana did some research, which had a profound effect on them.
"There is this actual footage from the exorcism, from the NYPD, that this movie is based on," she explained to HuffPostUK.
"When I saw this footage which is horrific, Eric didn't sleep for three weeks, I didn't sleep for a week, but that's only because I only watched five minutes of the 30 minutes. It's so horrific that it's something that will shake you to your core. It's not like something you'd find on YouTube, it's actual footage."
The stars were wary of being too sensationalist as they wanted to ensure they were telling the story in the right way, as it involves real people. While that was at the fore when things began, Olivia became concerned about something else as time wore on.
"The concern comes up with - if this really happened are we opening up some kind of portal that's not supposed to be here? Are we playing with the Devil too much?" she explained.
"I started the movie as a non believer but I finished as a believer."
The 34-year-old star was then quizzed on whether any spooky goings on happened on set. There wasn't anything too worrying, although the star had to try not to think about the film's premise too much.
"There was a moment where I was concerned. There was a moment when we were all on set and we were kind of talking about something and we had this moment of, 'Do you think we're all OK?' And we just shrug it off and keep going because the thought of it is too horrific," she said.
