By accident of course.  It was WEIRD.

The wire wheel buzzed the skin off of a swath of my hand maybe 1/16 inch deep, but left all the hairs standing.  It didn't start bleeding for several seconds, then little drops of blood started appearing throughout the trench, gradually growing and merging into a pool.  There wasn't any pain for about 15 minutes, then it hurt like a sonofabitch.

That was about 7 years ago.  It healed up pretty well, just a little visible scarring on the surface.

Now I always wear gloves when I use that machine.