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.

Qualley tells PEOPLE how the body-horror film, directed by Coralie Fargeat, pushed her to take risks onscreen Embodying her character in The Substance challenged Margaret Qualley to take new risks onscreen.

Obviously, between all of the scenes of spine-splitting, vomiting, close-up injections and Dennis Quaid chowing down on a plate full of prawns, the whole film wasn’t exactly a walk in the park, but there was really no preparing for the birth of Monstro Elisasue in the final act, was there?

Demi Moore tells PEOPLE she hadn't met Margaret Qualley before becoming her costar in Coralie Fargeat’s new horror movie 'The Substance,' but had enough 'indirect connections' that they 'felt like we

From daunting high-energy choreography to nine-hour prosthetic application, the stars tell EW "The Substance" was a satisfyingly grueling, months-long shoot.

Demi Moore, Margaret Qualley, Dennis Quaid and more stars hit the red carpet for the L.A. premiere of their film, 'The Substance.' See all the photos.