It was a long-running joke in actress and filmmaker Sarah Polley's family. Why doesn't she look more like her father? In her new documentary "Stories we Tell," Polley tries to get to the bottom of that mystery -- while also attempting to better understand her glamorous and free-spirited mother, who died when Polley was 11. But the greatest revelations in the new film involve the nature of storytelling itself. Polley joins us to discuss the film, which is showing as part of the San Francisco International Film Festival.