If you read the original paper (https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2026.1633599/full https://www.frontiersin.org/journals/ps

If you read the original paper (https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2026.1633599/full https://www.frontiersin.org/journals/psychology/articles/10....) then they go into more detail on the piles of pebbles and what got taken; the graphs in figure 4 (https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2026.1633599/full#fig4 https://www.frontiersin.org/journals/psychology/articles/10....) make it very obvious that the chimps loved the crystals. (an "euhedral" crystal is one with lots of obvious facets, an "anhedral" one is one that's been rounded down into a more pebble shape.)