The weird thing (for me) about snakes is that I don't see them right away most of the time.
The copperheads I killed (first one while hunting) was a couple feet from me when I saw it. I walked up a hill to look down on the fields on the other side and stopped as I got near the top. I was looking for groundhogs and not moving. As I looked back down at the ground in front of me (before walking over the top of the hill) I saw the copperhead in some tree limbs just to my right (small tree limbs.) Pulled the speed six out of my pocket and popped him.
It's a weird feeling to realize you almost stepped on a (poisonous) snake. Just another step or two. Be looking around at other stuff and then suddenly see that snake within feet of you.