I have seen several serious accidents from people sticking their hands or fingers into the arc of a prop. A couple of these required surgery, most required stitches. Always exagerate your movements around a prop. If you reach around a prop, If it's a 10" prop reach 20" around it, and remember to do the same thing coming back. Never try flipping the prop by hand. Always scrape the edges of a new prop to take off the sharp flashing on the edges. Again, never flip a prop by hand. Electric starters and 12V batteries are cheap, fingers aren't.