Nyong'o, 36, told Variety she modeled the guttural voice on a real medical condition called spasmodic dysphonia, which causes the voice box to involuntarily spasm.
"I studied that," the actress said. "I worked with an ear, nose and throat doctor, a vocal therapist and my dialect coach to make sure that I could do it and do it safely because I had two roles to play.
"... While I was practicing and figuring it out, I definitely scratched my throat a few times," she added. "By the time we got to filming it, I was pretty set on how it should go and I was very good at warming up my voice and cooling it down."
But some people who actually suffer from the condition are less than pleased it was used for scares.
"She is mimicking a neurological disease that destroys my life and thousands others," one person tweeted.
"I sooo appreciate my condition being used as inspiration for your evil character. Not!!!!! Ignorance rules!!" added another.
"I think anytime you bring awareness to a disease or a disorder, it's a double-edged sword," a doctor told Inside Edition. "It's very good for people to know more, but it's very difficult for people who have the disorder."
Nyong'o said she particularly looked at Robert F. Kennedy Jr., who suffers from the condition himself. In a statement, he defended the actress.
"I'm grateful to Lupita for shining the spotlight on an injury that's been starved for attention," he said. "In my discussions with her I've been impressed with by sensitivity and sincerity."