Pu o Hiro is a roadside rock in the Easter Islands, but at one time its value was so great that factions fought over its possession. The rock's natural holes allowed it to be played like an instrument. Rare Earth uses it as a starting point for discussing consensus value.
It is a stone aerophone, considered as an ancestral musical instrument of the Rapa Nui culture. It has a main hole through which it was blown, producing a deep trumpet-like sound. There are some islanders who are skilled at making it sound, which is not easy.
It is a unique artefact on the island and its use is not well defined. It seems that it was formerly considered a talisman for fishing. Certain traditions point out that when blowing in one of its holes, there was a loud audible sound to the region of Poike (3 km far away) that attracted the fish to the coast. It was also a war trophy, carried from one end of the island to the other at different times.
On the surface of the stone there are several petroglyphs with vulva forms ("komari"), the symbol of fertility, so it is believed that Pu o Hiro was used in rituals related to it. It is likely to have been an instrument of call, though it could also have constituted the center of a ceremonial site in honor of Hiro, since that area is very rich in monuments and engravings.
If this is interesting, you might want to look up the diamond-water paradox: