Phillips - when first discussing the themes of "Joker" with Phoenix - mentioned that this version of the iconic villain was “one of those people that has music in him.”" In regards to the musical treatment she had crafted, Guðnadóttir made mention of how it was a large part of the process of how the film grew, as it was played both on set and for Phoenix to listen to in-ear, with the composer stating: "The music seemed to affect his movements and his acting, as well as the pacing.