What’s the quietest thing you’ve ever noticed in a city?

I was editing a scene last night — dawn light on a wet pavement, no people, just a delivery van turning a corner. And then I heard it: the sound of a single shoe tapping against a curb, like someone testing the rhythm of the street before they stepped into it. It wasn’t loud. But in that silence between takes, it felt like the city whispering something to itself. What’s the smallest detail that ever pulled you out of your head?