In such cases, the discarnate soul experiences an irresistible impulsion toward the gross world and craves gross objects so badly that it seeks gratification of its desires through the gross bodies of those souls still incarnate. Thus, for example, the discarnate soul may want so much to drink alcohol that it takes to unnatural methods of gratifying the craving. It awaits its opportunity. When it finds someone who is a suitable medium drinking alcohol in the gross world, the spirit satisfies its own desire through that person by possessing his physical body. In the same way, if it wants to experience the gross manifestations of crude anger, it does so through someone in the gross world who is feeling angry.
Such souls are constantly waiting to harass incarnate persons with similar sanskaras, and they try to maintain their contact with the gross world through others as long as possible. In life after death, any lingering entanglement with the gross world is a serious hindrance to the natural flow of the soul’s onward life. Those who are subject to this precarious condition must be looked upon as particularly unfortunate, since they invite upon themselves and others much unnecessary suffering by seeking unnatural gratification of coarser desires through others who are still incarnate. Compared with these unfortunate souls, the posthumous life of other souls is much smoother.
-Discourses 7th Ed., 305