On this episode of "You Sang My Song," Katy Perry watches YouTube fan covers of her songs "Unconditionally," "Last Friday Night (T.G.I.F.)," "Dark Horse," "Roar," "I Kissed a Girl," "I'm Still Breathing," "Firework," "Chained to the Rhythm," and "The One That Got Away." Fans react to Katy watching their music.