My mind is exploding from this thread. I like it. No lawnmowers existed back when barbers were in circulation, at least gas mowers like today. Nowadays, there is a safety standard that has to be met by all mowers sold in the US; it limits the blade speed (rpm's) to a safe level. In other words, the blade "should" not be able to propel rocks or golf balls at a "deadly" speed.
I remember playing baseball one day in a back lot and a neighbor's riding lawnmower (about 50 feet away) struck a small rock propelling it past my head, missed by about 6". This was in the early 70's when the restrictions might not have been in place, I don't know for sure. That rock was whizzing by at deadly speed and I think it would have killed me if it hit my brain box. Nowadays, if you get hit by a rock from a lawnmower, theoretically it wont kill you.
Anyway, no lawnmower ever made could slice through a coin so cleanly. Coins like those shown (I have found one silver quarter and one 1890's Canadian cent cut cleanly) must have been sheared with tin snips or something similar.