It's always heartening to see an actor find their iconic role — one that perfectly fits their skills while also playing slyly on their public persona. Demi Moore has found hers with The Substance, the sophomore feature from French writer-director Coralie Fargeat (Revenge), which won a screenplay award at the Cannes Film Festival. This satire of Hollywood's obsession with youth is also the most outrageous body horror film I've seen in years. The deal In her prime, actress Elisabeth Sparkle (Moore) was a megastar. At 50, she's happy enough to host a daytime aerobics show — until the piggish network boss (Dennis Quaid) decides she's over the hill. Fired and adrift, Elisabeth crashes her car and lands in the hospital, where a nurse slips her a flash drive labeled "the Substance." It leads her to a storage locker where she finds a kit that promises to help her recapture her youthful physical perfection. One injection, and a gorgeous replica of the younger Elisabeth (Margaret Qualley) births herself from the older one's spine. Self-christened "Sue," Elisabeth's second self is eager to snag Elisabeth's former job and become a star in her own right. But the Substance has strict rules: The two symbiotic selves must switch places every seven days, with one remaining comatose while the other is active. If one perishes, so does the other. Elisabeth will learn that sharing a life with your younger self is trickier than it sounds — especially when she wants to replace you permanently. Will you like it? What is it about French women filmmakers and body horror? Julia Ducournau's Raw is one of the few films that have made me cringe in visceral repulsion; The Substance is another. Both these directors know that true horror involves far more than putting blood and guts on-screen. Longtime genre fans easily detach themselves from such imagery — unless the movie gives them an emotional connection to what they're seeing. The Substance somehow accomplishes this feat, despite not featuring a single conventionally sympathetic character. Fargeat's storytelling and visual style are glossy, hyperreal and cartoonish, almost to a Zack Snyder degree. The story takes place in an '80s-tastic version of Hollywood in which cellphones exist, yet the entertainment industry is still obsessed with TV ratings and aging stars revitalize their careers by doing aerobics. The characters are archetypes with scant backstory or inner life. They all have…