"Shake It Off" is a song sung by Reese Witherspoon (as Rosita) and Nick Kroll (as Gunter), originally sung and written by Taylor Swift. It is available on the Sing: Original Motion Picture Soundtrack.
In Sing, Rosita and Gunter sang this song as their final act in Buster Moon's singing showcase. Prior to performing her final act, Rosita can also be seen singing this song before falling flat on her face in front of Gunter and Buster Moon. In Sing on Tour, actors inside Rosita and Gunter costumes perform "Shake It Off" live.