In Jordan Peele’s new horror film, “Us,” Lupita Nyong’o plays Adelaide, a mom on vacation with her family, and Red, a demon who is essentially Adelaide’s evil doppelganger. Red’s eyes are exaggeratedly wide, and she is armed with a throaty, halting voice. Nyong’o says that the inspiration for her spine-chilling vocal delivery came from Robert F. Kennedy Jr.’s voice. When she heard him speak, it reminded her of what Peele was looking for — “scratchy” — in Red’s voice.

Kennedy suffers from the neurological disorder spasmodic dysphonia.

That’s a “symptom of different parts of the brain not working, which prevents a fluid voice,” says Dr. Andrew Blitzer, professor of otolaryngology at Columbia University’s medical school and an expert on the condition.

“SD is just a subset of dystonia,” says Blitzer of the general disorder that causes uncontrollable muscle contractions and spasms. The incurable ailment is rare, affecting an estimated 50,000 people in North America, according to the National Spasmodic Dysphonia Association.

Nyong’o recently told Variety that she decided to affect the SD symptom after learning that it’s caused by trauma, in line with her character Adelaide, who is alluded to having been damaged in childhood. “[SD] creates this spasming in your vocal cords that leads to an irregular flow of air,” said Nyong’o.

For those who suffer from SD, hearing that their affliction is inspiration for a terrifying character is upsetting. (Reps for “Us” had no comment.)

“When I read about it, I was angry; I felt mocked,” Margot Durkin, a retired educator from Alexandria, Va., who was diagnosed with SD in 2001, tells The Post.

“I don’t think her mistake was in method acting or in taking something she had heard and developing it into her character,” says Durkin, 70, calling Nyong’o “a very fine actress.”

“I’m faulting the way she talked about the voice that she took. She took the SD voice and made it sound as if she was demonizing the disability, that she was looking for something creepy and evil.”

Kim Kuman, executive director of the National Spasmodic Dysphonia Association, says that SD “is not a creepy voice; it’s not a scary voice. It’s a disability that people are living with and shouldn’t be judged upon . . . For so long, people were told that it’s psychological — and it’s not. It’s neurological. Stress is going to aggravate any health issue.”

Durkin, who was treated with uncomfortable Botox injections into her larynx, says that living with the disorder is a daily battle: “It’s a real disability that many people live with, and for some of them it is so severe it affects their ability to hold a job. And it affects your social life terribly. At a crowded restaurant or party, people can’t hear you; waiters bring you the wrong order.”

On Twitter, others issued their concerns. Cathy Graham was similarly dismayed, writing, “She is mimicking a neurological disease that destroys my life and thousands [of] others’.” Linda Walker wrote, “I sooo appreciate my condition being used as inspiration for your evil character. Not!!!!!”

The muse himself, RFK Jr., was more ambivalent, and toyed with the possibility that Nyong’o’s on-screen imitation was a form of flattery.

“Not sure what to make of this honor,” he tweeted. “Is it a good thing?”