about the spirit or ghost
i believe that life could exist as a form of pure energy. it means that people may exist in another form after death: spirit or ghost. but it is only possible for those with extremely strong spirit. for example, the resentment is probably one of them. the corresponding soul has a name: 'ghost'. for most ordinary people, after death, the soul exists for at most a few days or in less time, it will dissipate into free energy and its consciousness will be broken.
for the strong ghost, there may be such cases that it grab someone else's body. but it's not easy. the ghost and the living are a form of opposition. for example, water and fire, water overpowers fire, and fire can overpower water also. the winner between the two depends on whose energy is stronger. ghost lost its physical body, it must lost a lot of energy. if ghost want to grab someone's body, it will aim to someone weak. even a weak has certain resistance. so even if the ghost succeeded, it will loss more energy and be very poor during a period of time.
from a scientific point of view, this is as described in einstein's mass-energy equation: all existence is a manifestation of energy. people and ghosts are just a form of energy.