Re: Semper's reference to the sharp rock. I saw a documentary a while back that compared a flint edge to a scalpel. (I hope I get this right on the numbers). They said the scalpel had a 7mm edge and the flint's was 3mm. Much sharper. I was a bit surprised.
Re: Hop's paperclip story. An old weapon that was used by ladies were long hat pins for the very reason he outlined.

