Sound in film is added very consciously. When a film is building up to a big reveal, it might use suspenseful music. When it wants to appeal to your emotions, you might get sad music. Sometimes a voice-over is used with certain images, even though the person whose voice it is was also filmed for a talking-head shot. Why? What made the filmmaker decide that a voice-over would be more effective? What are they trying to achieve? And what other sounds are added to the documentary for impact?