78. Since obsession can never be caused by a good spirit, one essential point is that of knowing how to recognize the nature of the spirits who manifest. Unenlightened mediums can be deceived by appearances, whereas those who are prudent look out for the smallest signs of suspicion, and the spirit ends up withdrawing upon realizing there is nothing it can do. Prior understanding of the means of distinguishing between good and evil spirits is thus indispensable to mediums who do not want to expose themselves to being caught in a trap. It is no less indispensable to mere observers, who can thereby evaluate the worth of what they see and hear.