Bwiti ceremonies are lead by spiritual leaders called N'ganga. Oftentimes it is required to be initiated into secret societies prior to obtaining an education in medicine as many aspects of African medicine can only be communicated to initiates. Knowledge is passed orally through generations and is made up of both scientific and subjective disciplines. Initiated healers access the invisible realm to gain insight into the matter at hand. Invisible does not mean unknowable...it simply means that it is invisible because many subtle aspects of everyday reality are not looked for except with disciplined investigation. Similar to the way we flip a switch and our lights come on, to a trained electrician, the unseen is no mystery. But to those of us who are untrained it works like magic. Perhaps this is why traditional African healing was called witchcraft by outsiders.