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

Last week, I was cleaning a microfossil slab under the scope, and for about three seconds—just long enough to register—I swear I heard the faintest click. Like a tiny jaw snapping shut. Turned out to be my own breathing echoing in the silence. But now I wonder: what’s the quietest thing you’ve ever actually heard in a place where nothing should make sound? Not the hum of lights or the scrape of tools—something that felt like it shouldn’t exist at all.