Imagine high school kids watching the films of Whit Stillman, Noah Baumbach and Richard Linklater, perhaps even John Cassavetes, Ingmar Bergman and Eric Rohmer, who then go home and attempt to make films like these on their own, with their friends, in their basements and in their showers. The result: “Mumblecore.” The kids: Andrew Bujalski, (the often nauseating) Mark Duplass, Jay Duplass, Aaron Katz, Lynn Shelton, Joe Swanberg, Greta Gerwig (who seems equally comfortable acting in the nude or fully-clothed, I’ll give her that) and others… These films are interesting in that their focus is often on the subtle...