For years, the stars of "Mystery Science Theater 3000" found the funny in films that were never intended to be comedies. A poorly-written B-grade science fiction film like "This Island Earth" was, for instance, perfect fodder for the MST3K guys. On August 19, Michael J. Nelson, Bill Corbett and Kevin Murphy will be back in theaters for live RiffTrax presentation of "Reefer Madness." A notorious propaganda film from the 1930's, this over-the-top movie shows the horrors that come with smoking marijuana.