Sophie Okonedo and Oprah

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Sophie says she had to delve deep into her character to act out an intense range of emotions. "All her nerves are on edge all the time, and everything she feels is like a 100 watts up from everyone else," she says.

Sophie needed to be able to cry on a dime to play May, something she says you can only prepare so much for. "I just sort of stay very open and then just really listen and watch what everyone else does and then just react," she says. "I didn't really try and work out what I'm going to do. I do all the research, massive research before I start—but as soon as I get on the set, throw that all away and just see what happens. Just trust that it would happen."

The London-born actress had another challenge—to transform her British accent into May's South Carolina drawl. Sophie says she had an excellent dialect coach while working on the film but can't put into words exactly how she found May's voice. "It's divine intervention," she says. "I don't know—it's just part of acting. I've hardly used my own accent in any part I've done."