A squirrel, once. He bolted across my path on a steep fast road decent. He sort of grabbed the front tire as it ran over him, and that tossed him onto my upper body, where he scurried around for an instant before jumping/falling into the spokes of my rear wheel. Amazingly he was ejected from the wheel, apparently without too much harm-because he ran straight up a tree afterwards. The whole thing happened so fast I hardly knew what had happened.