The growing conditions for Ah Wei were said to be extremely stringent.
First, the deceased had to be a maiden. Only a virgin's body could preserve that wisp of pure Innate True Qi.
Second, she must have fallen ill and died suddenly.
If she had died from a prolonged illness, her body's True Qi would have long been depleted by the disease, making it impossible for Ah Wei to grow.
Third, she had to be buried in a treasured land with excellent feng shui, one that could keep the body from decaying for decades.
Finally, and most crucially, when the coffin was opened for excavation, the Ah Wei had to be found inside with the corpse.
All four conditions were indispensable.
Therefore, this kind of Ah Wei was an exceedingly rare, almost legendary miraculous herb.
The second theory was a bit more "down-to-earth."
