Diegetic sounds originate from within the scene and are naturally occurring, like character voices or object sounds. Non-diegetic sounds are added in post-production and don't originate from within the scene, like narration, music, or amplified sound effects. The distinction depends on the audience understanding of natural versus added sounds, and diegetic and non-diegetic conventions can be used to surprise audiences, as in comedies. Footsteps in a chase scene would be non-diegetic and recreated/amplified in post, to create a sense of panic for characters fleeing. Background music is also non-diegetic and meant to represent the teens' lives in the full film.