Holding the WD40 soaked rag on top of the chain near the sprocket and rotating the tire backwards. Don't ask why I thought this would be a good idea. The real kicker is that I did almost the exact same thing last week to my other hand while checking the belt tension on my Sportster. Just in case you were wondering, on a Harley with its belt and pulley you get more of a crushing action than the tearing you'll experience on a chain driven bike. Again, don't ask what I was thinking. Maybe I should leave the beers till after I finish the service.