Background music is music someone has on, but it isn't the main element in the room. What I mean by this is that the music is on, but there are other things people are focusing on.
Background music sets the tone and mood for the scene. If it's a sad scene where a character just died, the music would be more depressed and sorrowful. It just gives the mood a boost and helps people understand how the characters in the movie are feeling.
In the mirrored ball, the objects are varying sizes, which allows certain objects or subjects (ex: man) to appear closer and others farther away (window), creating depth and form.
