Iāve just read of interesting uses of kozuka/kogai of which I was totally unaware (āRoots Still Cracking Rocksā by Ellis Amdur, first edition. Publisher -The Ran Network p 67-68)
They were used as post-mortem āsign offsā (ātodome sandanā) for various types of killing by stabbing them into particular parts of the body and leaving the small blade in place. They affirmed to the authorities the reasons for the killing when the perpetrator actually presented themselves to the authorities for sanction:
GyÅichi (āat the will of a superiorā)-when killing by order of a superior, one stabbed the body through the sole of the foot.
Adauchi - when killing in the service of a vendetta (retaliation), one stabbed the body under the ear (āvendettaā has a nuance of obligation -one is upholding the honour of clan/family, for example.
Ishū-uchi - when killing for personal revenge, one stabbed through the solar plexus.
Amdur suggest these must be areas important in Chinese-based medical theory but all this information is unreferenced so I canāt attest to its truth.