If memory serves, one can smell them, the Copperheads...which is often sooner and or more reliable, than hoping to 'see' them ( in time).
Used to be lots of them where I played as a child, and, being able to smell them, I always was especially alert and careful to determine where they were and or to allow them a wide berth, or just to back away and take a different route.
They can be hard to see if they are laying still, for sure...