"My little dog... always recognized me. That's all that counted," joked Moore, who brought her Chihuahua dog Pilaf to the Cannes Film Festival this week.
Explicit body horror film "The Substance" has been a breakout hit, drawing boisterous cheers, wild shrieks and lengthy applause at screenings in packed theatres along the Croisette.
It tells the story of an ageing actress who, after being booted from Hollywood by chauvinistic male studio executives, resorts to a strange and mysterious technology that promises to make users "better in every way".
Known as The Substance, it allows those who use it to create a younger version of themselves -- one which is created in a highly disturbing and difficult-to-watch process.
Worse still, when misused, the technology leads to some of the most horrendous and ghastly deformities ever shown on the big screen -- requiring Moore to transform in astonishing and unflattering ways.
Moore underwent "six to eight hours of makeup" some days, and admitted that at times during the premiere she had felt she was "not watching myself".
"It was a very raw experience" that required her to "expose myself emotionally and physically," she added.
The film, which is in competition for the Palme d'Or top prize, co-stars Margaret Qualley as Moore's younger self, and Dennis Quaid as her crude, boorish boss.
It marks a stunning return for Moore, who starred in giant 1990s hits like "Ghost" and "A Few Good Men", but has been largely absent from the festival circuit for decades.
"I was so glad to be here to see the beginning of an incredible third act for Demi," said Quaid.
Moore is seen as a frontrunner for the best actress prize at a festival that has not been afraid to bestow awards on female-focussed horror films, including 2021's Palme d'Or winner "Titane".
"The Substance" is directed by French filmmaker Coralie Fargeat, who praised the 61-year-old Moore for not being afraid to reveal herself or risk being ridiculed.
She told AFP her film focuses on why society's attitudes to the female body are "problematic at a younger age, when it is not perfect or too big, and when it gets older."
"We are almost obliged to hate it, one way or another, and we can become our own torturer," she said.
Moore added that the film's message was "not anti-men -- we're just anti-jerks."
