Here are just some of the symptoms of demonic possession I have come across: growling, eyes turning and glowing red, different voices coming from the person, self harming, contorted facial expressions (once saw a guy literally smiling from ear to ear... a bit like the 'mouth' from Lord of the Rings), blasphemous remarks about Jesus, clawing at the ground, strong sulphurous smell, chang in room temperature, sense of oppression.. these are some that I have witnessed and dealt with.