I'll never forget deer hunting when I was about 19 years old, on our farm in northern Vermont.
Walking along, I heard a "zzzzip" that was quite loud and near. Hit the dirt in case another round was coming, but none did.
I heard the shot a few seconds later, the shooter must have been on the ridge at least a half-mile away to the west, and definitely couldn't see me.
Needless to say, it was a little unnerving. It definitely took my awareness of where I was shooting to another level as a result.