Matthias Schoenaerts spent two months boxing, doing MMA training on a daily basis and also doing weightlifting and eating junk food like burgers, ice-cream and pizza in order to gain weight and a little belly, because Jacques Audiard wanted Ali to look strong but not fit, a bit unhealthy because the character is poor, so he doesn't have the means to feed himself properly.
Marion Cotillard stated that she hates filming sex scenes, which for her are usually the worst part of being an actress, but for the first time she enjoyed her sex scenes in a movie with Rust and Bone. She said: "I am shaking; I feel very bad and I want to cry most of the time because I hate it so much, but here it was totally different. I was so involved with my character that I was happy she would enjoy something like that. It's a movie about love, about flesh, about rust and bone and heart and sex, so without the sex scenes the movie would have missed something".
The title "Rust and Bone" refers to the taste of blood in the mouth when, upon a blow to the face, the lips are crushed against the teeth.
Within minutes of her arrival for the first day of rehearsal at the Marineland in Antibes, in the South of France, Marion Cotillard was required to watch the whales perform for a crowd. "I was jet-lagged and sensitive," she recalls. A female trainer assigned to work with her on her character asked what she thought. "I didn't want to be disrespectful, but I said, 'I'm sorry, but I have to be honest - I hate this situation. I hate to see animals doing clown things. I think it's horrible', she remembered.
After starring together in "Rust and Bone", Marion Cotillard recommended Matthias Schoenaerts for her boyfriend Guillaume Canet's directorial-debut in Hollywood: Blood Ties (2013). Canet has said that he chose Schoenaerts after hearing Cotillard praising his acting several times.