I reached down to grab a piece of wood to place into my campfire years ago and felt this unbelievably jarring pain go through my thumb (considering how gently I had placed my hand down to grab the piece of wood, the level of pain was immense).

There was a very tiny piece of something stuck in my thumb, which I was able to remove but not able to inspect very closely as it was pitch black outside and I was working with a flashlight.

I wrote it off as most likely being a splinter of glass from somebody's smashed beer bottle that had gone straight through my skin.

Reading this, however... it was much more likely a metal bristle from somebody's cheap camping brush that they used to clean their camping grill.