One time in the jet boat over 20 years ago the alternator belt was slipping. So I got out the toolbox and adjusted the belt, put the tools away made one last "check" of the belt tension, yep, nice and tight, shouldn't slip, right at that exact moment my brother hit the key to start it thinking I was done. I yanked my finger out, but it was too late, my finger ended up as the prybar between the belt and the crank pulley to pry the nice and tight belt right off, the engine didn't start because I yelled and he immediately turned the key off. That hurt something fierce, I looked down and the belt was laying on the bottom of the boat, and I looked at my throbbing finger and saw blood flowing so much I couldn't see where it was coming from. Turns out the crank pulley crushed right through my fingernail, all the way across, right in the middle of it. So all the blood was coming out through the middle of my fingernail. It didn't feel too good, my hand was shaking and throbbing as I was trying to assess the damage, but I kind of got lucky too, that belt was tight, could of been much worse.