Naomi Watts and Matthew McConaughey found a sweet way of preparing for their film "The Sea of Trees."

"We didn't have any time to prep [for the movie] so when Matthew reached out to me via email," Watts told Vogue Australia. "I said, 'Do you mind if we write to each other in character?' And he wrote back and said, 'Write at will, Joan.'"

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Watts plays McConaughey's wife, Joan Brennan, in the Gus Van Sant film, which follows the life of suicidal American, Arthur Brennan (McConaughey), as he befriends a Japanese man lost in a forest near Mt. Fuji. Together, the two men search for a way out.

"So we proceeded to create this relationship through letters. Some would be just a few lines or something fairly benign, and then other times it would be a long letter about how we failed and how we need to change and accusations of giving up; the same old story, your classic marriage problems," Watts explained. "Sometimes we would write poetry, sometimes love letters, sometimes stormy letters, sometimes I would leave a voice recording [as Joan] knowing he was going to be shooting in the forest that day. It was great."

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While the 46-year-old actress seems excited for "The Sea of Trees," the film did not get the warmest of welcomes at the 68th annual Cannes Film Festival. During a press screening, the movie was met with both laughter and boos -- and this is not a funny film.

"I liked the experience of making it and I'm glad we got the opportunity to introduce it to the world," McConaughey said during press conference following the screening. "Anyone has any right to either boo or ovate."

The film is expected to hit theaters later this year.

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