Vanessa Hudgens and Jimmy Fallon have turned the happy-go-lucky Friends theme song on its head. On The Tonight Show Monday, they performed a slow, acoustic cover of "I'll Be There for You." "We are friends," Fallon introduced the number. Their voices harmonized softly and smoothly like a lullaby. The original, sung by The Rembrandts, sounds like a comedic testament to life's ups and downs, especially when set to scenes from the sitcom. But this rendition is a heartfelt ode to friendship. They sang in honor of Hudgens' new show Powerless, which premieres Thursday, February 2 on NBC. Friends also ran on NBC on Thursday evenings, Fallon pointed out. It's a tough act to follow, but at least she's got the music down pat.