When Anthony Ranere dug up the eggplant-sized stones in the Central American tropics in 1973, he knew at once from their blunted edges that someone had used them, over and over again, to pound things to a pulp.
But what was being pounded?
He guessed that the stones were ancient kitchen tools - used to mash edible roots that forest-dwellers had gathered long ago.
Turns out he was only partly right.
Pretty good article.