[Braska starts off by bowing his head in greeting.]

Then... Their souls linger on in the world. Over time, they will come to envy, and then resent, the living. In this hatred, they find the will to create a new body, and will return to the world as monsters to enact their anger upon those still alive.

This... is not always the case, as there are sometimes exceptions. But it is what normally happens on Spira.