Watching one's step

Do you ever wonder what makes you look down just as you are about to step on a dangerous spot? I've had a few close calls with poisonous snakes over the years. Once I somehow managed to 'step on air' inches above a cottonmouth coiled on my path. It was on a remote island and I was wearing flip flops - help was many hours away. I was walking toward a pond which had my attention, but somehow in the split second before my foot hit the snake (and I would have been bit) I got some warning, saw it, and managed to hold that foot in the air as my other one stepped over the snake. A couple days ago, Crystal and I were helping with a park cleanup. Right in Crystal's path was this tiny pigmy rattlesnake carefully camouflaged in shaded grass. From it's perspective, all it could do is coil up, flare it's jaws, and shake it's tiny tail like mad as the giant's feet approached. No where to run. No where to hide. She was scanning for trash but somehow spotted it before both of them would regret it. I was lucky enough to have my camera nearby and waited for the sun to get above the trees and light up the snake. It was tricky trying to photograph too. With my telephoto lens, I had to be too far away to avoid grass blades blocking my view... but with a more standard lens, I had to get right down on the tiny snake to adequately fill the frame and it didn't like that one bit.