Warning: Spoilers ahead! We’ll be addressing major events and the ending of “The Substance” (now in theaters), so proceed with caution if you haven’t watched it yet.

Margaret Qualley proves she can embody terrifying roles when necessary.

Demi Moore went through intense makeup transformations in the body horror film “The Substance,” where she portrays a former TV fitness star who resorts to a black-market drug to regain her youth. However, it’s Qualley who dons a special prosthetic suit for the film’s shocking and gory finale, portraying a character that is as hideous as she is beautiful.

“It was a challenge,” Qualley shares. “I had an amazing team of prosthetic artists who helped put it on and take it off, providing laughs even when I was close to losing it.”

In the film, Elisabeth Sparkle (Moore) finds herself ousted from her job as her sleazy employer (Dennis Quaid) seeks a younger alternative. In desperation, Elisabeth chooses to undergo an elaborate DIY treatment to become “more perfect.” This results in a younger version of herself (played by Qualley), leading to a shared existence that alternates every week – seven days for the older body, followed by seven days for the new one, and the cycle continues.

Adopting the name Sue, the new persona quickly ascends to fame, becoming a network darling and even landing a gig to host a New Year’s Eve live special. Sue revels in the glitzy lifestyle, complete with parties and handsome admirers, and soon starts to crave more time outside of the one-week constraint. She begins bending the rules by siphoning extra “Stabilizer” fluid from Elisabeth’s back, much to Elisabeth’s frustration as she starts to deteriorate physically the longer Sue disrupts their arrangement.

When Sue runs out of fluid, she reluctantly hands control back to Elisabeth, who opts for a “Termination” serum to eliminate Sue. She initially administers the shot but immediately regrets it, reviving Sue, only to end up killing Elisabeth out of spite. Sue then prepares for the New Year’s show, but her body crumbles, culminating in her desperate need for the same “Activator” drug that created her.

Enter Monstro Elisasue, a hybrid creature that combines both women and surprisingly embraces her appearance, revealing a complex perspective on beauty. Qualley emphasizes a poignant moment where Monstro adorns herself with an earring on what is essentially the front of her face—one of the more bizarre features of Monstro being Elisabeth’s screaming face apparent from her shoulder.

“It was significant to connect with Monstro’s essence, experiencing a deep emotional moment despite her bizarre form. Oddly enough, I found Monstro to be stunning,” Qualley reflects. “The contrast between the internal struggle and the external appearance was incredibly moving.”

Qualley dedicated up to six hours to get into the Monstro makeup, which restricted her mobility significantly. “I could barely see out of one eye, couldn’t hear, couldn’t move my arms, and the retainers were enormous, making it tough to speak,” she elaborates. “It was a demanding role to fill. Yet, the sense of purity in her character was refreshing, especially after spending four-and-a-half months portraying Sue, who lacked any real depth.”

Moore reflects that “the script simplifies certain elements, but once you’re in the makeup, you have to forgo eating, you can hardly drink, and you need incredible self-discipline.”

Monstro takes center stage in the film’s wildest scene at the end, during which she goes onstage at the New Year’s broadcast. The audience is thrown into chaos as they are showered in blood from Monstro’s exploding and regenerating physique.

According to Qualley, around 30,000 gallons of fake blood were used, with director Coralie Fargeat handling a firehose for the effect. Qualley even sent videos to Moore showcasing the madness happening on set. “I had the only week off from filming,” Moore chuckles. “And then I ended up with shingles.”

Although Monstro doesn’t receive a happy ending—she escapes but dramatically explodes all over Elisabeth’s star on the Hollywood Walk of Fame in the concluding scene—Qualley did keep some of that experience with her: wearing the Monstro suit led to a breakout of acne on her face, which is visible in the next in her role for “Kinds of Kindness.”

“I hadn’t fully healed. Even six months after, I still felt like Monstro was a part of me,” Qualley shares. “But honestly, I kind of enjoyed how it looked, so that was fine.”