The drum used by chöd practitioners is made out of human skull, not of wood; human bones are also used to make their wind instrument. The places that they choose to do their practice are often haunted. All these seem impervious to reason for the general public, especially the exoteric Buddhist practitioners. The intent is to infuriate the spirits by deliberately showing contempt and provoke them into retaliating with thunder, lightning, and other such terrifying signs, because practicing emptiness under great stress is more conducive to eradicating self-grasping. Granted, such practice should only be done after attaining realization. If not, there may be more harm than benefit by just imitating others.

~ Depicted from "THE HANDBOOK FOR LIFE"S JOURNEY : On The Three Poisons - How to Confront Anger