I thought some people might find this interesting.
A couple of months ago, I accidentally shoved the broken end of a glass tube pretty deep into my finger. I felt it hit something, but wasn't sure at the time if it was fingernail or bone.
As it turns out, the broken tip carved a semicircle in my fingernail while it was still 1/4" from emerging, back in my finger (the tube went in at a relatively shallow angle).