The term "demonologist" is one being seen more frequently, however, it does not always mean the same thing. This most serious form of paranormal investigation requires careful handling and much caution. Call them "demons", "evil spirits" or "dark entitites" - they all spell trouble for the people involved and to the potenital investigators. They are known to often endanger those who study or investigate them. They frequently provide such a strong negative influence that the only word possible is "possession." There is an excellent article about this subject at TAPS. The article explores issues of professionalism, study, and how to handle the religious beliefs of others in demonic cases.