The following article examines the use of sound in Xavier Dolan's 2014 film Mommy. While powerful soundtracks that heighten the emotional impact of his films have become Dolan's trademark, the soundtrack in Mommy – here understood in Michel Chion's sense as the composite track containing voice, music and sound effect–marks a new stage in Dolan's development and in sound design in general. Dolan not only adapts the duration and editing of scenes to the duration and rhythm of a song, but also molds his scenes around certain songs. Music indeed drives his melodrama and orchestrates the protagonists' ups and downs, while the plasticity of the human voice underscores important developments and highlights crucial reversals. In the famous Wonderwall scene, in which the aspect ratio extends from 1:1 to widescreen, music literally invades the movie theater. Dolan's soundtrack not only opens up new realms of subjectivity and belonging, but also unsettles our sense of perception and hints at deeper implications of the technological set-up. Mommy ultimately calls into question the ontological bond between a sound and its originsand exemplifies the dualistic nature of film sound, that is, the split between voice and image, and the process of grafting voices onto a body.