The Descendants recently won an Academy Award for Best Adapted Screenplay. In the movie, Matt King, played by George Clooney, is dealing with a lot. His wife is in a coma, his kids are out of control, and he's coming up against something called the Rule Against Perpetuities. What is this legal rule that is central to the plot of The Descendants? We speak with Randall Roth, the legal adviser to the film.