Had my turn with a grinder a week ago. Wearing the traditional Chinese safety boots, the only thing I was missing was the cardboard box taped on top...
Must have grabbed what I was cutting and jumped straight out of my hand, took a nice bit out of my right foot, only just missed tendons, didn't quite go deep enough, gave my second toenail a nice trim too, lol. 4 stitches later and of course I need to wear boots for work so it hurts like hell putting socks and boots on and off...
Worst thing was I had boots on before it happened and had finished and then decided to touch a bit more up, of course with thongs on and that's when it happened... Murphy's Law at its best ....