Acorn Grinding Holes, "Kitchen Rock"

A rock used for gringing acorns and washing out the tannic acid to remove the bitterness. It took seven soakings to remove it all to make it edible. It seems likely that one would start with dry shell removed acorns at the bottom and mash them in water, drain, and move them uphill. The acid would shape the rock from use over time and make the undercuts. This had been used for thousnds of years. Source: Objaverse 1.0 / Sketchfab