When I’m walking, if there’s a pothole in the sidewalk, or if I miss the sidewalk and step onto slightly lower grass, my foot twists inwards and I come down on the side of my foot. This twist occurs incredibly fast. I just need a half-inch declivity to trigger a ninety degree twist. I sprained my ankle many times this way when I was young. It could be just a bad habit, but I think of it as a useless instinct. If this behavior is imprinted in my DNA it could be very ancient indeed; that foot-twist might save my life if I slipped while climbing a tree.