We love Jimmy Fallon [1]'s classroom instruments series, but honestly, we never anticipated Metallica would agree to it. Sure, Adele did it [2]. So did Idina Menzel [3] and The Lonely Island [4], but Metallica? They're too hardcore for that . . . right? Nope! The metal band rocked out with Fallon and The Roots on Wednesday to the tune of "Enter Sandman," and it's actually pretty glorious. Take a look!