Was regluing the hypalon to the hull on my RIB, using an angle grinder to remove the old glue from the aluminum. Holding the hypalon down with one hand and maniplulating the grinder with the other. Didn't take into account the rotational friction, and as I made contact, the wheel ran right across the top of my free hand. Inspected the damage (painful, but not severe), changed from holding the hypalon with fingers to thumb, and did the same damn thing again, across my palm. Would have been really pi$$ed (and in pain) bu I was laughing too hard at my stupidity. Hard to explain how I angle ground both sides of my hand.