Flesh-spades [noun]: Fingernails.
This phrase is fairly self-explanatory, but I found it quite unique. I can guess that one of the reasons that we phased it out of our lexicon is due partly to the aversion to the word flesh, but also to the advances in our technology. So rare is the time when we as humans would need to use our fingernails to dig without the assistance of a shovel or other instrument.
The substitute, frustrated with a boorish classroom bellowed in fury, his voice, a splitting sound akin to flesh-spades on a chalkboard. (Doesn’t have the same ring as nails, I suppose)
Kacirk, Jeffrey. The Word Museum: The Most Remarkable English Ever Forgotten. New York: Simon & Schuster, 2000. 75. Print.