"Bellyache" is a song by American singer Billie Eilish. The song was released on February 24, 2017, through Darkroom and Interscope Records. It was written by Billie Eilish and Finneas O'Connell, with production by O'Connell. "Bellyache" is a midtempo electropop song, with R&B, hip hop, deep house and Latin macabre influences. Lyrically, the song is written from the perspective of a psychopathic murderer. The Marian Hill Remix was released on May 5, 2017.