Any or a combination of the following behavior pattern is indicative of spirit or demonic possession:
1. Hearing voices directing the person to perform acts he may not have considered doing.
2. He or she will frequently see or sense the image of the possessing spirit as it existed in its physical life.
3. The victim may blackout or faint without knowing what transpired during that time.
4. Sometimes, in the midst of a conversation, he may have a mental block and act in a trance-like manner.
5. He may be observed talking or walking differently or acting in a strange, irrational manner.
6. He may act in a way he has never done before. His friends may see him as a totally different person.
7. In a worst scenario, the possession may reach a climax where the person may commit a crime, some violent or anti-social act and even suicide.
8. He or she may speak in tongues, and perform lewd acts and avoid religious objects (like a crucifix, rosary, etc.) (Rense.com)
