We’re off to never-never land, and by never-never land we clearly mean a small Tonight Show dressing room, where Jimmy Fallon and the Roots managed to wrangle heavy rockers Metallica into a lively classroom-instruments performance of “Enter Sandman.†Look at James Hetfield on the toy clarinet! And Lars Ulrich on the Fisher Price drum set! Just don’t be deceived — the song will still most certainly give you nightmares, even with the medley of fun kazoos.