In Springfield: Marge's sister Selma marries mobster Fat Tony; Smithers helps Moe turn his tavern into a trendy gay bar. Tommy Chong and Homer team up for a comedy act. Beyond Springfield: An earthquake and tsunami hit Japan, killing thousands; Prince William weds Kate Middleton; Osama bin Laden dies; 33 trapped Chilean miners escape to the surface. Notable guests: Stephen Hawking, Mark Zuckerberg, Daniel Radcliffe. Season rating: 7.28 million viewers.