With 2004's Medulla, Bjork's already distinctive musical vision is catapulted into another stratosphere. Using the mouth as the primary instrument - vocal, percussive, and otherwise - Medulla evokes the ethereal sound of an angelic spirit and a group of Benedictine monks desperately hurtling through outer space. Pleasure Is All Mine immediately establishes Medulla's haunting, yet strangely comforting, tone. On top of a distorted background of carnal breathing, the vocals of Bjork, Inuit throat singer Tagaq, Mike Patton (Fantomas / Mr. Bungle), and the Icelandic Choir combine with the rhythms of human beat-box Rahzel, building to an eerily ferocious intensity. The album, which also features art-rock pioneer Robert Wyatt, shifts back and forth between ambitious, operatically layered tracks (Where Is the Line and Desired Constellation) and more direct a cappella songs (Show Me Forgiveness, and Oll Birtan). Bjork reaches her peak when she combines both of these seemingly disparate forces, as in the electrifying Who Is It (Carry My Joy on the Left, Carry My Pain on the Right) and the album-closer, Triumph of a Heart. Medulla proves that, once again, when it comes to sheer musical audacity, Bjork knows no boundaries.