Possessed is the wrong word.
I think what you probably mean is mesmerized, as Nina Harker was by Count Dracula. (She was forced to drink his blood.) In such a condition all that is required is that the person be isolated from the influences of the vampire and the bodies immune system will eventually over-come the contagion.
If the person is under the vampire's control then you have to do everything you can to distract the person, excite his metabolism so that he must take (retake) personal responsibility for his conduct, force him back into the real world. Bright flashing lights seems to be a particularly effective stimulant.
There is no such thing as a vampire possessing a human. A vampire can make a human into somewhat of a "slave", but they can't possess them.
find him or her sucking a cow's blood. no... the vampire should be really thirsty and attempt to suck the non-vampire friends' blood.
No. But you should really blink from time to time.
Well what ever you want on your profile its your game and person, although I would recommend a bat or vampire!
There has been some speculation that a vampire is a dead body possessed by a demon. This is emphasized in the book Dracula.
A soothsaying spirit or a person who is possessed by a soothsaying spirit is known as a pythogenesis. This is a term from the New Testament of The Bible.
We should give them the blood or sharp teeths. Give them a person so they can suck blood.
To be a vampire, any person simply has to be bitten by another vampire but not killed. If a vampire kills a person completely they die, but if they don't die, they become a vampire themselves.
i think it is possible
Genius
A soothsaying spirit is a supernatural being believed to have the ability to foretell future events or provide guidance. A person who is possessed by such a spirit may be considered a medium or oracle, acting as a conduit for communication between the spirit world and the physical world.
The legal consequences for killing a possessed person would depend on the circumstances and laws of the jurisdiction involved. In most cases, claiming that the person was possessed would not be a valid legal defense for taking another person's life. It would be treated as a criminal act subject to prosecution.