The heart.
According to Han Dong's earlier observation of the "Corpse-Thorns",
he confirmed the existence of the Thorns Heart and that the heart was a critical organ, even capable of performing brain-related functions, far more important than the heart is to humans.
[The Head] for these Sacred Level Lives seemed more like a display of abilities rather than a fatal area.
In the recent battle, Han Dong had Magic Eye Wide Open, carefully observing the heart of Tailor-Lu, and could basically ascertain that his heart was a fatal spot.
He even hypothesized that for Sacred Level Lives, the heart was an essential organ, crucial to the foundation of life.
However, damage to the heart wouldn't necessarily be fatal.
...
As the core of energy supply, the heart controlled the hub of the Original White Line.
When it was pierced by Han Dong's sword, the [White Flesh Apostle] immediately disintegrated, turning into a pile of scattered white flesh and slack white lines.
