They extracted tears from the ox's eyes to make a special fluid, after which they would dab fresh willow leaves in it and wipe it over both eyes, a method known as the Heaven Eye Technique. At that point, they could clearly see ghosts and malevolent entities.
However, this kind of Heaven Eye Technique was considered the simplest and most superficial method within the Taoist magic arts.
Against some powerful ghosts or evil spirits, it could easily become ineffective.
Truly formidable Immortal Masters would directly use their mana to perform the Heaven Eye Technique, rendering even slightly stronger ghosts unable to hide before them.
And there were even more powerful practitioners who cultivated a third divine eye, transforming it into a Divine Skill.
Individuals like Wen Zhong and Yang Jian were outstanding representatives of such Divine Skills.
