Exorcism is an ancient practice involving the expulsion of demons from a possessed person's body. The person performing the ritual is referred to as an Exorcist, and is usually a high ranking member of his/her church. While exorcisms are more commonly associated with the Catholic church, exorcisms are performed in almost every religion that involves the belief in evil spirits.
Many doctors believe that a person who is labeled possessed may actually suffer from a particular mental illness. For those who are successfully exorcised, science attributes their cleansing to the power of suggestion and/or the placebo effect. That is; their beliefs are so strong that the ritual will actually trigger a remission in whatever mental illness they suffer.
As a child, the mentally ill Ben Foster ("With Friends Like These...") had an exorcism performed on him by his community church at the behest of his mother. Years later, while being plagued by hallucinations which continually commanded him to kill, Ben sought out a priest to perform another exorcism, but was rebuffed.
- Gabriele Amorth, An Exorcist Tells His Story. San Francisco: Ignatius Press, 1999. Vatican's chief exorcist tells about Roman Catholic practice of exorcism with numerous anecdotes from his own experience.