We have been talking about motherhood for just a few moments when Juliette Binoche starts to cry. She is recounting a documentary that she saw, she thinks in 1998 when she was in London, about an old woman who had survived the sinking of the Titanic. "She was talking about what happened to her when she was a child. She was on the boat, and it sank and there were little boats to save some people, and she was in there and her mother was there with her and all of a sudden..." The words have been tumbling out, but then her voice cracks and she trails away to nothing and, astonishingly, she's in tears. Esther Addley reports.