This angry and persuasive piece of agitprop by writer-director Richard Linklater (Before Sunrise, A Scanner Darkly) and writer Eric Schlosser, adapting the latter’s nonfiction book of the same title, isn’t simply an account of how shit gets into our hamburgers. It’s also about Mexican immigrants who sneak across the border and wind up enslaved (or literally ground up) by meat packers, teenagers who work for fast-food companies and want to fight the system but don’t know how, and many other social as well as environmental factors. Many reviews have suggested that this is as politically mild as a John Sayles movie, but Linklater clearly agrees with the frustrated kid who says, Right now, I can’t think of anything more patriotic than violating the Patriot Act. The strong cast spelling this out includes Ashley Johnson, Patricia Arquette, Luis Guzman, Bruce Willis, Kris Kristofferson, Greg Kinnear, Ethan Hawke, and Catalina Sandino Moreno (Maria Full of Grace). R, 114 min. (JR)