This week the US Supreme Court heard oral arguments in US v Stevens, by some measures the most momentous free speech case in decades. The strangest thing about the case is that it arises from a law passed to keep women from stepping on mice. The second-strangest thing is that the Justice Department is fighting to keep that law on the books.

In 1999, agitators claimed there was a fad for “crush videos”. These showed women stepping on the heads of mice and rats while talking dirty, something that titillated (or so it is alleged) a certain class of viewer. In a panic, Congress passed a law that made it a crime to profit from any depiction of a living animal being “intentionally maimed, mutilated, tortured, wounded or killed” in a way that is illegal under federal or state law. Clearly, the law is too broad. As written it could get you jailed for selling a hunting video in Washington, DC (where hunting is illegal), or screening a bullfighting movie anywhere.