Two different scenes were shot when the thief played by Juan José Ballesta stole the wallet. One where he did do it and one where he didn't. Director 'Jaime Marqués' said that didn't decide if he stole it until the editing.
The music played at the first sequence is the so-called "Symphony of the Sorrowful Songs" by Henryk Mikolaj Górecki. The lyrics are based on a goodbye poem that a Polish kid painted for his mother on the prison wall he was shortly before died.
The post-coitum conversation was written moments before shooting it and it's actually filmed on the production company with a mattress and a sheet on the floor because the original house couldn't be used at that moment.