Bandha-kaarana-shaithilyaat pracaara-samvedanaac ca cittasya para-shareeraaveshah
By the relaxation of the cause of relationship to the body, and the experience of going forth, consciousness is able to enter another body.
A mind that lives in ignorance identifies itself and is attached to its physical form, the body. By reversing that identification and loosening the hold of the Pancha Kleshas or Five Afflictions of Man being Avidya (ignorance), Asmita (ego), Raaga (attraction), Dwesha (repulsion) and Abinivesha (clinging to life) one is able to loosen one’s hold on the physical body. One’s mind is then freed and as mind is more subtle than Prana itself it can then direct it. Further if one has developed intimate knowledge and experience of the Nadis, the psychic pathways in which Prana travels within the subtle body, one is able to transfer by the effort of will his/her Prana through the Nadi system of another body as Prana systematically enters and exits the body on a consistent basis which keeps it alive. In other words it is the projection of one’s consciousness through the agency of Prana into another’s physical abode via the Nadi system.
With this Siddhi, one is not only able to influence the thoughts and moods of another but with its mastery the ability to even bring back to life very recently deceased animal and human bodies, except that now it is one’s consciousness operating through them.
Why not use this Siddhi to gain freedom from the body at the time of death instead of inhabiting another cage made of flesh.