I've been finding a lot of half-acorns lately.
This was a rediculously productive year for the red oak tree in my yard. In October, there was a solid carpet of acorns on the ground beneath it, and that was after an entire garbage bag was carted away for other uses (feeding woodrats). The squirrels (and my sheep) have gradually thinned out this acorn layer until there is now mainly just a carpet of acorn shells below.
But there are also chunks of acorn meats. Lots of them. Mostly the lower (pointier) half, with the upper (fatter) part missing, chewed off. Each morning I've been gathering these meats and feeding them to the sheep - about enough to fill my two cupped hands. And by the next morning there is a whole new crop of nut meats for the gathering.
My theory was that the fat end of the acorn (the part that is missing from most of the meats) might be more nutritious. Maybe during super mast years, the squirrels just eat just the good parts and leave the rest. Kind of like the brown bears that eat just the skin of the salmon. But this diagram (below) makes it seem like the fat end isn't so different from the pointy end, and the pointy end even has more goodies, like the root. But you never know. In any case, this phenomenon (if it happens in the woods, too) probably provides a steady source of acorn meats over the winter for other animals during big mast years. Even when the squirrels have hidden them all last fall.