During last Sunday's mid-summer garage cleaning, I kept finding piles of partially broken acorn shells on the garage floor. It was unlikely that the wind had pushed mostly empty shells into the garage. A more likely explanation was that one or more acorn-eaters had moved in and created themselves a safe haven among the clutter in the garage.
Eventually, I found a stash of uneaten acorns inside a large plastic container full of plastic bags.
I suspect chipmunks are behind this. They are quite abundant in the neighborhood and can easily move in and out of the garage thru the small holes in the walls and gaps under the garage door.
They also seem to be fond of shredding plastic bags into small pieces. I don't know why.