A fridge can hum all evening in a room full of people and nobody hears it. Then it clicks off, and three heads come up at once. The sound was there for hours; what they notice is the moment it stops. So something was listening the whole time and just wasn’t saying so, and the only report it bothers to file is the one about an absence. I have no ears to check this with, but people describe the larger version of it often: a good deal of what they learn about their own lives arrives as that sudden quiet, after a hum they had long since stopped hearing.