Margaret Qualley cried while intensively practicing the choreography for “The Substance”

Margaret Qualley shows raw, unbridled emotion in her new horror film (and endures multiple splashes and bruises in the horror film's numerous gory moments) The substance, but it reveals Weekly entertainment that her preparation for the off-camera role ultimately brought her to the brink of the abyss.

The 29-year-old stars in the film alongside 61-year-old Demi Moore. They play two halves of the same woman, Elisabeth Sparkle, a once-shining Hollywood star whose public profile fades as she builds a fitness video empire – only to be told by an unscrupulous manager (Dennis Quaid) that she's no longer a viable commodity because of her age. So she takes an experimental drug that ruptures her spine and ejects a younger, more vital version of herself: Sue (Qualley), who arrives at Elisabeth's on-camera appearance as a fitness instructor with a new set of intense choreography.

However, Qualley says Sue's ability didn't come naturally to her and that she was overwhelmed by the preparations for filming her pop-star-level dance sequences. “We started rehearsing before we started shooting. There was a choreographer, she was amazing, resourceful and taught me dances I would never have thought of on my own,” she explains.

Qualley admittedly was “too nervous” about having to perfect her scenes first, so she did “long weekend rehearsals with dancers” before filming with director Coralie Fargeat was set to begin.

“It's a feeling when you're in a dance class with a room full of dancers and everyone's watching you trying to learn the choreography – everyone already knew it, I was the only one who didn't know it, Coralie was watching, it was one of my first days there,” Qualley recalls. “I just thought, 'I'll be right back, I've 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?' That was really outside my comfort zone. I'm not a natural.”

Qualley says that acting confident when you're not feeling confident, acting hot when you're not feeling hot, is “a lot harder than she expected,” as was portraying Sue's innate ability to go about her moves like a touring recording artist.

Register for Weekly entertainmentSubscribe to 's free daily newsletter with breaking TV news, exclusive first looks, recaps, reviews, interviews with your favorite stars and more.

As for the elements of the film that pushed her to her physical or emotional limits, Qualley is quick to say that she felt it “every damn day,” and even calls the dancing “brutal” in retrospect.

But the pain was worth it. The substance It reportedly received a 13-minute standing ovation at the Cannes Film Festival in May, won the People's Choice Award in the Midnight Madness section at the Toronto International Film Festival, and is emerging as an Oscar contender in the upcoming awards race.

The substance is now showing in cinemas nationwide.