The holy grail hold the "water of life" and also the "blood of christ" In church you eat the body of christ to be more like christ, therefore who is christ? The people who eat his body?
Where on earth is there life giving water, and blood from people who eat the host? The womb of women.
On another forum a poster said the draco's inpregnat and then eat the unborn fetuses along with the period blood once a month. So when does a soul enter a new body? Probably right around that time. But if the soul has to adjust to the shape of the new body, then it may be in a coercive state, in which if this state is taken advantage of and manipulated to soul could be forced to take to a new body, such as the draconians body.
This is a theory I'm posting just to data mine.
The last tarot card is a dragon with peoples faces in it.