A fan, refrigerator or distant engine may disappear from your attention while dialogue becomes absorbing. When conversation stops, the background sound can suddenly feel prominent again, even if it never actually stopped.
Choose a scene with a steady environmental sound. Listen once for its presence beneath the voices and once for the moment you become conscious of it. These are different observations: attention changing is not the same as a documented change in the soundtrack.
If the sound clearly cuts out or returns, note its timing relative to the image. Does it coincide with a door closing, a character leaving or an edit? Keep an unexplained sound unexplained if the film never supplies a source.
In a fictional kitchen exchange, the last line might leave only the refrigerator hum. The sound could make the room feel ordinary again, or emphasise how uncomfortable its silence has become. Its effect depends on the exchange, not a fixed rule that humming means loneliness.
Avoid turning the listening exercise into a volume test. Use a comfortable level and replay a short section if needed. A strong film note describes the transition from conversation to environment and then explains what that transition did to your sense of the room.
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