hmmm, i never thought I'd hear of this again....my father is missing the top of his right thumb from this very thing. He was cleaning his chain with the motor 'helping out', and the rag got caught in the sprocket and took his hand for a ride. They didn't reattach fingers back then, but he actually regrew a decent amount of it back (which sounds crazy, but even the docs were impressed), and he has a decent excuse for a fingernail too. needless to say, I don't clean it this way, and I don't advise anyone doing the same.... glad to see this guy got most of his fingers back, though.