The third eye is not really a part of the physical body. It is part of the second body which is etheric body. Your etheric body is a body which is similar to your physical body over which it is superimposed, it has a corresponding spot in the physical body, but it is not part of it, so far the closest reference scientist discovered on psychical body is the Pineal Gland.
A ghost is a consciousness whose body has dropped but not the mind. And the mind demands a body, because all desires and passions of the mind can be fulfilled only through a body. Its mind wants to touch some lovely body. If you are weak and without any will, some ghost can push his way inside you, because it does not have a body and its desires are burning.
Talks from the series "Can the mind observe without comparison?". This Talks goes deeper on how does it happen that deep layers hidden in consciouness can be exposed?, Comparison between 'what is' with 'what has been' and 'what will be', is the process of fear and Can the mind observe without comparison?. This is J Krishnamurti's Sixth small group discussion in Malibu, 1970.