Lupita Nyong'o says her latest film Us took an "emotional" toll on her and it was "exhausting" playing two different versions of the same character.
"This movie stretched me, it bent me, it cost me a whole lot," she told Dotty on the Radio 1Xtra breakfast show.
Us is a horror film written and directed by Oscar-winner Jordan Peele - the man behind Get Out.
In the movie a family of four - the Wilsons - are confronted by monster versions of themselves.
Lupita plays mum-of-two Adelaide Wilson and a scarier version of the character called Red.
To make Red sound distinctive, Lupita says she mimicked a voice condition called spasmodic dysphonia.
"It's a condition that's brought about by trauma, sometimes emotional, sometimes physical and sometimes inexplicable," she said.
"It's where your vocal cords start to spasm and they create this irregular abrupt pattern of air.
"So I had experienced someone speaking with that condition and I got curious about it."
'I was told to gargle salt water'
Lynda Clark, from Nottingham, has the condition and told Radio 1 Newsbeat she first noticed it when she was at university.
"I started to find it was really hard to speak during the discussions, I had to put in a lot of effort to get my voice out."
She says it took her a while to get diagnosed because the condition usually affects people who are a lot older.
"I was told to gargle salt water and to drink hot water by doctors, but eventually a junior doctor said it sounds like something neurological and not something to do with your throat."
Lynda says she has Botox injections every three months to help her voice.
"I've got the type that makes your voice sound breathy rather than sound strangled and sometimes I have to put in a lot of effort in to speak."
For the film, Lupita says she met people with the condition and worked with a voice therapist - to make sure she didn't damage her vocal cords.
The star also says she decided to stay in character when playing Red on set.
"I went a little more method than I usually do where I stayed in the vocal posture for the whole day and I would remain isolated in a room festering."
The actress is no stranger to taking on complex roles - she won an Oscar for playing the character Patsey in the film 12 Years a Slave.
But she says she had to let out her "inner monster" while making Us and reached "breaking point".
"It was technically very challenging. We're playing against ourselves. The way in which things had to play out was so specific.
"It took its emotional toll on me. I definitely had a moment of rupture while making this movie."