A friend of a friend had this happen to their son over the weekend. Father was mowing (not sure with what, or if the gaurd was on or off, or how far away) but a stone came off the blades and struck him in the forhead. Hes been in and out of a coma with a fractured skull and internal bleeding / pressure on the brain. They're worried about the pressure causing oxygen deprivation and brain damage. Pretty scary, its bad enough breaking a window or hitting a car.... Would be a good reason to invest in a OCDC.