How ‘The Substance’ Pulled Off That Bloody, Gloriously Disgusting Ending With Demi Moore and Margaret Qualley

SPOILER ALERT: This s discusses plot details of " The Substance ," in theaters now.

The final act of Coralie Fargeat's "The Substance" has the internet in shock, and might just be one of the wildest 20-minute rides in recent times.

Special effects artist Pierre Olivier Persin explained that Fargeat wanted to use practical effects, instead of digital CGI, where possible. "70-80% of what you see is practical," Persin told Variety.

Demi Moore plays Elisabeth Sparkle, a faded Hollywood superstar relegated to hosting fitness videos reminiscent of the 1980s. Sadly, the producers want someone younger and search for a new host to replace her. Overhearing the conversation, Elisabeth comes across an opportunity to try a drug that promises to enhance her into a better version of herself. But it comes with strict and specific instructions. Elisabeth injects herself with the slime-green substance, and ends up birthing a younger version of herself – Sue, played by Margaret Qualley . Sue lands the fitness job, and the town becomes obsessed with her. Meanwhile, every seven days, without exception the two need to switch. And of course, things go downhill as Sue gets a taste for the adulation, the success and the youthfulness. As Sue sticks around for longer than her seven days, Elisabeth starts seeing the consequences, beginning with a dead and aging finger. It only gets worse. By the end, Sue needs to stay in her body longer so she can host the New Year's Eve party celebrations – but with Elisabeth's body already depleting and aging, Sue finds herself desperate. She injects herself with the serum which specifies a one-time use only. Sue/Elisabeth morph and birth Monstro Elisasue, a mutated version of both of them.

Persin spent over a year working on the film and the final design, going through many iterations. "We did tons of designs and used everything from computer-generated sculptures to Photoshop to traditional sculptures and drawings to find the character that Coralie liked," Persin told Variety.

In the end, he found himself using a traditional maquette to sculpt what the morphed entity would look like.

Monstro Elisasue, as she was called had puncture holes and more than one spine. In one version, Fargeat told Persin how she loved how he had designed the Monstro's spine, and she wanted him to add more spine. But it didn't end there. Said Persin, "She said, 'Maybe we can add teeth, biting one of the boobs.' So, I added that. It was as if we put Sue in a shaker and shook her body."

Due to time constraints, Persin subcontracted the build of Monstro Eliasue's suit to a U.K.-based company. "We had two full suits, one for a stunt double, and a half-built suit for Margaret, which she wore for closeups."

Persin and his team took care of all the effects, including the boob that squeezes out of one of Monstro's many holes.

The highlight of the scene is the obscene amount of blood that sprays the audience that has come to see Sue at the New Year's Eve show.

For that bloody mess, Persin had a special blood rig built by Jean Miel, the film's special effects coordinator. "We put that inside the suit, and it was like a fireman's hose that would spray blood – there was blood everywhere."

For Monstro EliaSue's last moments, Qualley was inside the half-suit for Monstro's last closeup moments. She wore a cooling vest, similar to what racing car drivers wear. "It had a cooling system that would inject cold water to cool her down," Persin explained.

In the build-up to Monstro EliaSue, there were various stages the Moore went through, each one was given a nickname on the shooting schedule. Said Persin, "We had the 'Requiem' stage, as in 'Reqiuem for a Dream,' that was the first stage with the half face. And we had a Gollum stage, I did a maquette design where she had a bent back, but that was straightforward," Persin said.

However, it all begins with the finger. As a starting point to show something was wrong, it was important Persin get it right. "I thought it was too big at first. It looked fake and funny. So we started again. Coralie came into the workshop or I'd send her videos, but we did a ton of designs for each stage. It really was about trial and error and starting over to make it better."

In total, Moore's makeup took anywhere from 45 minutes to six and a half hours. The longest application was when Elisabeth had aged, but because she was in the shower, Persin had to apply "arm prosthetics, full leg prosthetics and a full face prosthetic." But for Persin, it wasn't as simple as applying prosthetics — he also had to apply blue veins and spots because Fargeat wanted the decaying to "look like poison." So it was a matter of adding more blue to the veins. In the end, Persin found, applying them like fake tattoos, printed from a Photoshop file, worked the best and was the most effective.

As for the birthing scene, Persin admits he didn't have a visual reference when he first read the script. Initially he wanted to build a big puppet that could be mechanically operated. "They were sophisticated puppets," Persin said. "We wanted to keep it simple and use our hands or devices to keep it organic because that was important for Coralie. So, we used a full back prosthetic on the actress, and we added all the complicated effects at the end of the shoot," Persin revealed.