Msgr. Rossetti

Response: There are varying ways to describe different types and levels of demonic afflictions such as temptation, vexation, oppression, obsession, and possession. In different parts of the world, these and similar labels are used slightly differently, but all basically describe the same realities. In answering this question it is important to recognize that demonic afflictions are not in discrete categories but rather they gradually vary in intensity. 

Full possession might be the label for the most intense demonic affliction; the least demonic affliction is called temptation- we all experience the latter. Some extraordinary demonic afflictions that do not constitute full possession are typically called obsessions, vexations, oppressions or some cases might be called partial possession. When someone is partially possessed, the demons, when they are manifesting, show some control over the person's body. In response to deliverance prayers, the person who is partially possessed may twitch and jerk; they may have demonic scratches or bruises; they may have unusual illnesses or unexplained severe pains. But, despite these demonic afflictions, the demons do not take full control of the body in a case of partial possession. 

When the person is fully possessed and the demons are manifesting, the person's personality will recede into the background and a demonic personality will come forward and take complete control of the body. The person's face and personality change into a demonic personality, and the demons often will speak through the mouth of the possessed. In these cases of full possession a solemn exorcism is warranted. In lesser cases, perhaps called partial possession, intense deliverance prayers are likely sufficient. But in both cases, it may take some time to expel the evil spirits.