Well, in my experience, hunting cottontails teaches you to pay attention to your subconscious. At first, the only fuzzbutts you see are the ones disappearing into the brush ahead of you. Eventually, you start to see one or two here and there. You keep it up and get your eye calibrated by enough time in the field and you'll pick an eye out of a cover so thick a tick would struggle to climb through. Then the edge of an ear, here and there the curve of their back, etc.
You are seeing them, you just aren't "seeing" them. Stick to it! Spend a little more time standing still and scanning. Plus the standing still sometimes makes 'em jumpy, pun intended, and they'll scoot a hop or two.