Some cultivators, after battling Gui Tao's people, glimpsed the deathly pale, slightly decayed flesh of their bodies, only for their Taoist Heart to collapse, becoming mere puppets.
Thus, one must not look, listen, smell, touch, or even think.
Otherwise, a medium for planting devils would be created. Unknowingly, one's Sea of Consciousness would be seeded with the embryo of Demon Thought, transforming into fertile ground for its growth, ultimately leading to death under the "Planting Devil in Taoist Heart" technique...
And cultivators who died under the Planting Devil in Taoist Heart technique varied greatly.
For those with low cultivation realms, a mere glance was enough to taint their Taoist Heart, sparking mutual slaughter.
The assorted minor Demon cultivators encountered along the way were all killed like this by the Uncle;
For those at slightly higher realms, Demon Thoughts parasitized through close contact.