SPOILER ALERT: This article covers the plot details of “The substance”, now in theaters.

The final act of Coralie Fargeat’s The Substance shocks the internet and may be one of the wildest 20-minute rides in recent memory.

Special effects artist Pierre Olivier Persin explained that Fargeat wanted to use practical effects rather than digital CGI wherever possible. “70-80% of what you see is practical,” Persin said Diversity.

Demi Moore plays Elisabeth Sparkle, a faded Hollywood superstar relegated to hosting fitness videos reminiscent of the 1980s. Unfortunately, the producers want someone younger and are looking for a new host to replace her. When Elisabeth overhears the conversation, she stumbles upon an opportunity to try a drug that promises to transform her into a better version of herself. But it comes with strict and specific instructions. Elisabeth injects herself with the slimy green substance and ends up giving birth to a younger version of herself – Sue, played by Margaret Qualley. Sue gets the fitness job and the town becomes obsessed with her. In the meantime, the two must swap every seven days without fail. And of course, things go downhill when Sue gets a taste for admiration, success and youthfulness. When Sue stays longer than her seven days, Elisabeth begins to feel the consequences, starting with a dead and aging finger. It only gets worse. In the end, Sue has to stay in her body longer so that she can host the New Year’s Eve party – but since Elisabeth’s body is already exhausted and aging, Sue is desperate. She injects herself with the serum, which can only be used once. Sue/Elisabeth transform and give birth to Monstro Elisasue, a mutated version of both of them.

Persin worked on the film and the final design for over a year and went through many iterations. “We did a ton of designs and used everything from computer-generated sculptures to Photoshop to traditional sculptures and drawings to find the character that Coralie liked,” said Persin diversity.

In the end, he used a traditional model to shape the appearance of the transformed unit.

Monstro Elisasue, as she was called, had puncture holes and more than one spine. In one version, Fargeat told Persin how much she liked the design of the Monstro’s spine and that she wanted him to add even more spine. But that wasn’t it. Persin said, “She said, ‘Maybe we can add teeth that bite into one of the breasts.’ So I added that. It was like we put Sue in a shaker and shook her body.”

Due to time constraints, Persin commissioned a British company to make Monstro Eliasue’s suit. “We had two complete suits, one for a stunt double and a half-finished suit for Margaret, which she wore for close-ups.”

Persin and his team handled all of the effects, including the chest bulging out of one of Monstro’s many holes.

The climax of the scene is the obscene amount of blood splattered on the audience who have come to see Sue at the New Year’s Eve show.

To create this bloody mess, Persin had Jean Miel, the film’s special effects coordinator, build a special blood device. “We put it in the suit and it was like a fire hose spraying blood – there was blood everywhere.”

For Monstro EliaSue’s final moments, Qualley was in the half-suit to get Monstro’s final close-up shots. She wore a cooling vest similar to the ones racers wear. “She had a cooling system that injected cold water to cool her down,” Persin explained.

Leading up to Monstro EliaSue, there were several phases Moore went through, and each one was given a nickname in the shooting schedule. Persin said: “We had the ‘Requiem’ phase, like in ‘Requiem for a Dream,’ that was the first half-face phase. And we had a Gollum phase, I designed a model where she had a hunched back, but that was straightforward,” Persin said.

But it all starts with the finger. As a starting point to show that something was wrong, Persin felt it was important to get it right. “I thought it was too big at first. It looked artificial and weird. So we started again from scratch. Coralie would come to the workshop or I would send her videos, but we did a lot of designs for each stage. It was really about trial and error and starting over to make it better.”

In total, Moore’s makeup took between 45 minutes and six and a half hours. It took the longest when Elisabeth was aged, but because she was in the shower, Persin had to apply “prosthetic arms, full prosthetic legs and a full prosthetic face.” For Persin, however, it wasn’t so easy to apply prosthetics – he also had to add blue veins and spots because Fargeat wanted the decay to “look like poison.” So it was all about adding more blue to the veins. In the end, Persin found that the best and most effective way was to apply them like fake tattoos printed out from a Photoshop file.

As for the birth scene, Persin admits he had no visual reference when he first read the script. Originally, he wanted to build a large puppet that could be controlled mechanically. “They were sophisticated puppets,” Persin said. “We wanted to keep it simple and use our hands or devices to hold it organically, because that was important for Coralie. So we used a complete prosthetic back for the actress and added all the complicated effects at the end of filming,” Persin revealed.