Cameron Diaz tells ET's Thea Andrews all about her surprise "engagement" at Comic-Con and dishes alongside co-star James Marsden and writer/director Richard Kelly about their upcoming psychological thriller 'The Box.'

"I'm very excited because I'm getting married. I've accepted a marriage proposal from one of the fans," Cameron jokes with Thea.

But the conversation takes a chilling turn as the star dishes about her movie 'The Box,' arriving Oct. 30, in which she plays a wife and mother who receives a mysterious wooden box: One that can grant her instant riches, but will take a complete stranger's life in exchange. So, will she use the box?

"It's about the repercussions of your decisions, and the consequences of them," Cameron says. "It's your moral base, your moral root that decides something so drastic like this."

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