Speaking at the drama's Cannes Film Festival press conference, Stewart said that playing the teenage bride of Garrett Hedlund's Dean Moriarty was "emotionally stimulating".
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"I love Marylou, as a character she's very vivid, she jumps right off the page and smacks you in the face with her tongue. Not in a bad way!" Stewart said.
"She never sold herself, that was one thing about her that was really very different from everybody involved in that movement. She wasn't rebelling against anything, she was so just being herself."
"It wasn't her priority to be a part of something that was moving other people; it was just about the people that she loved. She's so completely human, she never made herself a commodity. I think if you were to choose one character that embodied the spirit of this book it was her.
"She really is this amazing link between the two boys (Sam Riley's Sal and Dean) - it's a grand statement to make, but it might not have happened without her."
Discussing her time in "Beatnik bootcamp", Stewart added: "I got to live more in those four weeks - for me in my normal life - more than I did in a lifetime. It was great."
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Photo gallery - 65th Cannes Film Festival in pictures:
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