Marlon Brando, smoking during the making of "A Streetcar Named Desire," 1951. Credit: PictureLux/The Hollywood Archive What people see on screen can shape what they do off it. When actors such as James Dean and Marlon Brando lit cigarettes in 1950s rebel films, smoking came to signify cool, defiance and desire for an entire generation. Among 12- to 17-year-olds in the US, smoking initiation rose from about 20% in the early 1950s to roughly 35% to 40% by the mid-1960s, according to retrospective data from national surveys . Screen media do not simply reflect society. They can also influence how people think about health , risk and behavior. Film and television reach vast audiences, embedding health-related behaviors in dramatic storylines. Medical dramas such as Grey's Anatomy and ER have brought hospital life into living rooms around the world, shaping public ideas about medicine and, for some viewers, even inspiring careers in health care . Sometimes films become accidental public health educators.…