Metallica busted out an unexpected cover song during Sunday night's show at Gillette Stadium in Foxborough, MA. Bassist Robert Trujillo and guitarist Kirk Hammett decided to play the least heavy-metal song imaginable: Neil Diamond's "Sweet Caroline". Trujillo joked "This song is really scary, super-heavy, and if you start moshing, try not to injure yourselves." "Sweet Caroline" has a special meaning in Massachusetts - the Boston Red Sox play it at every home game. Metallica's M72 tour moves on to Chicago's Soldier Field later this week.