Margaret Qualley shows off raw, unbridled emotion (and endures several splatters and squishes via the horror film's copious gory moments) across her new horror film The Substance, but she reveals to Entertainment Weekly that her off-camera preparation for the role is what ultimately brought her close to the brink.

The 29-year-old co-leads the film with Demi Moore, 61, as two halves of the same woman, Elisabeth Sparkle, a once-shining Hollywood star whose public profile dwindles as she mounts a workout video empire — only to be told by a ruthless executive (Dennis Quaid) that she's no longer a viable commodity due to her age. So she takes an experimental drug that forces her spine to split open and expel a younger, more vital version of herself, Sue (Qualley), who comes for Elisabeth's gig as an on-camera fitness instructor with a new set of intense choreography.

Qualley, however, says Sue's prowess didn't come as naturally to her and that she became overwhelmed while preparing to shoot her pop star-level dance sequences. "We started rehearsal before we started shooting. There’s a choreographer, she was great, inventive, and taught me dances I never would’ve come up with myself," she explains.

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Admittedly, Qualley "was too nervous" at the thought of perfecting her scenes at first, so she "did weekend rehearsals for a long time with dancers" before shooting was set to commence with director Coralie Fargeat.

"There's a feeling when you’re in a dance class with a room full of dancers and everyone is watching you trying to learn the choreography — everyone already knew it, I was the only one that didn’t know it, Coralie was watching, it was one of my first days there," Qualley recalls. "I was just like, 'I’ll be right back, I got this!' I just went to the bathroom and started sobbing and [then] was like, 'Do you think we could do this one-on-one for a while?' It was really outside my comfort zone. I’m not a natural."

Qualley says that "to act confident when you don’t feel confident, to act like you feel hot when you don’t feel hot, is so much harder" than she anticipated, and, thus, so was portraying Sue's innate ability to attack her moves like a touring recording artist.

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On the elements of the film that pushed her to the physical or emotional limit, Qualley quickly says she felt that "every goddamned day," and even calls the dancing "brutal" to look back on.

The pain was worth it, though. The Substance received a reported 13-minute standing ovation at the Cannes Film Festival in May, won the Toronto International Film Festival's People's Choice Award in the Midnight Madness program section, and isshaping up to be Oscar contender in the awards race ahead.

The Substance is now playing in theaters nationwide.