Well this is something that i have delt with quite a few times in my life, i have seen it on many occasions and each time it happens i rely on god only, it is only his power that can drive out demons, iv come face to face with someone who was possesed, and i tell you its one of the worst things that someone who isnt used to it can see. My friend and i went to a friends house who was having some trouble and little did i know someone else tagged along, well my friends friends showed up and wouldnt leave then her personalitly changed all of a sudden, which is a clear sign of possesion. Well as well as taking care of what was in the house i had to exorcise my friends friend, you see i was showing my friend and training him, just as im being trained. Well in the end god drove the demon out of her after some threats and snarls and lets not forget the animal sounds my friends friend made. If you ever have an encounter like this just rely on god and he will protect you!!!!

God bless always