This document discusses different categories of sound that can be used in thrillers, including diegetic, non-diegetic, and special effects sounds. It explains that diegetic sounds come from visible or invisible sources within the story, while non-diegetic sounds do not originate from the film world, such as voiceovers or background music. The document also discusses parallel and contrapuntal sounds and provides examples of how they can build tension or conflict with the visuals. It concludes by noting the filmmakers' intent to use various sound techniques like contrapuntal music to scare the audience in their psychological thriller.