Mani stones and carved yak skulls

Mani stones are stone plates, rocks and/or pebbles, inscribed with the six syllabled mantra of Avalokiteshvara (Om mani padme hum, hence the name "Mani stone"), as a form of prayer in Tibetan Buddhism. Mani stones are intentionally placed along the roadsides and rivers or placed together to form mounds or cairns or sometimes long walls, as an offering to spirits of place or genius loci.