Couple years ago, I had been cleaning up stuff underneath a car with a wire wheel. A few pieces must have come off. Couple days later, the back side of my shoulder was sore and when I looked, it had this infected spot. After inspecting it I noticed what looked like a splinter and pulled out a 3/8 metal bristle. Felt good to pull that out!
That's basically what happened. Last week I hit the old brake drums with the wheel so I could paint them. Picked up the bristle today.