I feel that the physical body mimics the soul etheric body that is within it by way of electrical impulses and bio-hydraulics. As long as the physical mechanical body is living it will be able to follow and mimic the actions of the soul. If the brain dies, the heart stops and the hydraulics no longer work. If the soul chooses to sit up the physical body simply is unable to follow. I dont believe that the body can trap the soul but the soul could probably choose to stay with the body in hopes of being revived.