After Green Day withdrew from last weekend's Voodoo Music Experience in New Orleans, Metallica stepped up to take their place, and acknowledged the switch onstage. Before the metal heroes tore through the Ride the Lightning cut "Creeping Death," they dove into the first 40 or so seconds of Green Day's "American Idiot" with uncanny accuracy. "That's all we had time to learn," joked frontman James Hetfield. Maybe thinking about their next album has them all tied up.