CANNES - Robert De Niro famously gained 27 kilos (60 pounds) to play the boxer Jake LaMotta in "Raging Bull" while Leonardo DiCaprio slept in an animal carcass and ate raw bison liver in "The Revenant".
But few actors have gone as far as to live on the streets to research their role.
That is what Singaporean director K. Rajagopal asked of the star of "A Yellow Bird", his film which touches on some of the wealthy city-state's most sensitive issues of race, migration and sex.
Rising television star Sivakumar Palakrishnan spent his weekends living rough on the streets of Singapore's "Little India", exploring a rarely seen side of one of Asia's most ordered societies.
The delicately drawn arthouse movie, which premieres Wednesday at the Cannes film festival, follows an ethnic Indian man - or a "black devil" as one of the film's Chinese characters calls him - trying to rebuild his life and family after a spell in prison.
"I made him go out and live and sleep in the streets because he doesn't come from that side of the tracks," director Rajagopal said.
"It was quite tough for him but he did it. I wanted a fresh response, for him to feel what it was really like to be homeless. That is why I like him so much as an actor, he's very open and intense."
The film, which is showing in the Critics' Week section of the world's top film festival, also touches on the "simmering tensions beneath the skin" of Singapore's supposedly harmonious multiracial melting pot.
The struggling ex-con Siva has to sleep on the kitchen floor with his mother because she has rented out the bedroom of her tiny apartment to mainland Chinese migrants.
"This is not unusual," the director said. "People rent rooms to foreigners to make money to pay the rent.
"It is very, very common, particularly among poor Indians. One of the great things about Singapore is that we are given a government-subsidised home, but 90 percent of us live in flats that are like pigeon-holes."
It also touches on another taboo subject - interracial relationships - throwing Siva together with a young migrant Chinese mother (Huang Lu) who is forced into prostitution.
"It's really unnatural to see an Indian and a Chinese person together like this in Singapore, especially with someone from China, especially because he is so dark-skinned. It doesn't really happen."
Rajagopal admitted that many may be shocked by his portrayal of his homeland.
"I was going for the underbelly, the marginal, because Singapore has a reputation for being modern and ordered. But there is this other side. It is a reality too."
But perhaps the most sensitive subject the film deals with is the place of the country's Indian minority of which Rajagopal is a part.
"I am seen as a foreigner in my own country. When I get into a tax office they ask me, 'Where are you from?' I was born here. But any Indian is not supposed to be Singaporean but foreign," he said.
"It affects your whole personal emotional space. Both Indians and Chinese are of migrant stock, and yet we are not very accepting of the new influx. We say these new Chinese are not like the Singaporean Chinese. I wanted to reflect that, which is also now a global issue with migration."
Rajagopal, 51, who has had a long career as actor and documentary maker, said "many people in Singapore will not agree with me on the whole racism thing. They will say it is not there. Even the minorities shy away" from the subject.
He said all Singaporeans take an oath at school to defend its multiethnic make-up. "We stand by racial harmony, it is a pledge we all take."
But despite that there is racism, the director insisted. "It is not in your face, it is simmering under the skin."