Many year ago I read a novel set, I believe, during either the first or Second World War on a German submarine. I can't remember many details about it but one thing that has stuck in my mind is that the crew of the boat had sharpened their thumbnails and carved serrations in them so they could be used in fights amongst themselves and when in brawls on shore. Was this ever a real thing or was it purely an invention?
The informal rules for bare knuckle fighting in colonial Virginia allowed for eye gouging, and some of the most notorious fighters supposedly grew their thumbnails long and would harden them with a candle flame for this purpose. I've never heard of gouging thumbnails outside of that context, but the idea isn't a pure invention either.
e- Here's a Virginia law from 1752 that makes it a felony to deliberately gouge someone's eye out:
I. WHEREAS many mischievous and ill disposed persons have of late, in a malicious and barbarous manner, maimed, wounded, and defaced, many of his majesty's subjects, for the prevention of which inhuman practices:
II. BE it enacted, by the Lieutenant-Governor, Council and Burgesses of this present General Assembly, and it is hereby enacted, by the authority of the same,That if any person or persons, from and after the first day of June, which shall be in the year of our Lord, one thousand seven hundred and fifty three, on purpose, shall unlawfully cut out, or disable, the tongue, put out an eye, slit the nose, bite or cut off a nose, or lip, or cut off or disable any limb, or member, of any subject of his majesty, in so doing, to maim, or disfigure, in any of the manners before mentioned, such his majesty's subject, that then, and in every such case, the person or persons so offending, their counsellors, aiders, and abettors, knowing of and privy to the offence as aforesaid, shall be, and are hereby declared to be felons, and shall suffer as in case of felony.