In Buddhism, we use bone in spiritual practice because the more we appreciate death, the more fruitful our life will become. We begin to live life differently and accept that death is inevitable, while the path to the end of this life is about service to others, loving all, and being happy (our the pursuit of happiness) in each moment, through the good and the bad. Bone is used as a constant reminder of death helping practitioners remember that life is impermanent. This is to help keep from getting caught up in petty concerns (Career, Social Status, Wealth) that mean nothing once this current incarnation is over. Another reason for the constant use of bone is that, in certain tantric rituals in Tibet, practitioners must offer themselves up to malevolent spirits and actually let their selfhood (their ego) be killed. This rather extreme step is considered an important sacrifice in the quest for enlightenment. The yak is an important animal in Tibet, the tribespeople will honor them in this life and the next.