Chimpanzees Throwing Rocks at Trees: Ritual, Spiritual, or Just Clean Fun?

One commonly observed behavior of some chimpanzees is that they like to throw rocks at trees--especially resonant trees that produce a deep, full sound. But why? New research questions whether it is a ritual at all, and especially whether it is indicative of emerging spirituality: https://www.newsweek.com/chimp-throw-rocks-trees-communication-1477637. The original journal article may be found here: https://royalsocietypublishing.org/doi/10.1098/rsbl.2019.0747 (access required)