What’s the quietest thing you’ve ever heard in a room?

I was coaching a kid who’d just missed her final shot in a sprint race. We were in the empty range building, and after she said ‘I’m fine,’ the silence hit like a wall. Not even the hum of the heaters. Just that one breath between us. I’ve never heard anything quieter. What’s the quietest thing you’ve ever noticed? Not loudness — the absence of it.