> Mystery of 2 million-year-old stone balls solved
> Here's how ancient cave dwellers used these stone
> balls.

Correction, here is how SOME cave dwellers used stone balls.

[www.lithiccastinglab.com]
Schick and Toth (1993) refer to Spheroids as an:----especially enigmatic artifact form that prevails throughout much of the Stone Age in the Old World in a globular, battered piece of stone called a "spheroid," "stone ball," or "bolas stone." As the result of experiments in stone tool making, in Zambia, they were able to show that Spheroids could easily be produced as a result of four hours of percussion---. without any necessary intent or predetermination. (1993)"
Heavily battered hammerstones arrive at their spherical shape from hammering. It would be impossible to know specifically how any one hammerstone might have been used. Any one of the smaller hammers could have been thrown as a weapon, used to process food or even, in the case of Spheroids, used as bolas stones.

From article above:
[www.livescience.com]
"Secondhand discovery
The ancient stone balls were covered with a shiny layer caused by exposure to the elements over time, Assaf said. Curiously, this mother-of-pearl-like layer was different from the layers found on the other stone tools in the cave, suggesting that "the balls were exposed to a different environment for a very long period and then collected by the cave inhabitants and brought inside."

In effect, it seems that the ancient Qesem Cave inhabitants were reusing these stones, much like second-hand shoppers.

"The Qesem people specifically selected these ancient, ready-made tools that somebody knapped before them (perhaps from older sites), probably due to their specific round morphology," Assaf said. "It wasn't a random choice — they brought them to the cave especially for bone-breaking activities."

IOW, the data they have does follow that those particular spheroids were used as they claim, but the problem is they are only looking at the *last* operation...the embedded bone particles, not the first operation or original primary intended use... "secondhand" as they said.
Example: I have an old screwdriver that I've used for notching bifaces, a punch, mini-pry bar, opening paint cans, and to stir the paint after opening the cans. If I were to look at the screwdriver under an electron microscope afterwards (and after wiping it off with a rag to clean it for storage in my tool box), what would I find? The evidence from only the *last* operation, not the evidence from the fact I also opened the can of paint with it also or 20 years ago to drive a screw, which would not have left a visible trace under a microscope. In fact, I've used that particular screwdriver for many operations other than it's intended original use since.

IMO, the authors are off to a good start, but have a long way to go to find every possible use for Spheriods, if that is even possible.