James Miller, a theater professor at the University of Wisconsin in Stout, is a fan of Firefly, Joss Whedon's short-lived science fiction series. Evidently Lisa A. Walter, the school's chief of police, is not. After Miller put a Firefly poster on his office door last September, Walter removed it, explaining in an email message that "it is unacceptable to have postings such as this that refer to killing." She claimed the poster was not covered by the First Amendment, since it "can be interpreted as a threat." Senior Editor Jacob Sullum explains what happened next.