Mathieu Amalric has admitted he struggled with Benicio Del Toro's working method while making their latest film Jimmy P: Psychotherapy Of A Plains Indian.
The Munich star plays a maverick academic counselling Benicio's Native American war vet in the film, and during shooting Benicio didn't like to socialise off the set, or to rehearse.
But Mathieu revealed in Cannes how his co-star's methods became clear when he saw the film.
"During psychoanalysis, the words surprise you. You don't know why these words are coming out. But an actor is supposed to know his lines by heart, so you have this paradox. I didn't understand it. I understood it after seeing the film."
The film was shot in Monroe, Michigan, which 47-year-old Frenchman Mathieu also found a challenge.
"There was nothing there. Nothing," he said. "It was very intense, and the situation of the shooting itself made it even stronger, the fact that we would live all together in a hotel where there was nothing to do. It was very close to the situation they were living in the middle of nothing."
Mathieu confessed before making the movie, psychoanalysis "frightened me so much that I rejected it, because my parental culture that told me maybe psychoanalysis had to do with weakness.
"You are not supposed to show weakness. You are supposed to 'be a man'. That's what my father would think of psychoanalysis."
But he revealed through filming the movie he discovered "a world of adventure: of research, of physical danger and how the body and the mind expand."