Yang Yan probably used this sort of poorly mastered technique.
Then Li Piaoqing lowered her head and continued working on the face in her hands, slowly slipping the blade into the slit she had just cut. "The second method is like this-making a human-skin mask. It requires highly sophisticated, specialized skills, as well as months and years of work. Each mask is custom-made for its wearer, allowing only one particular person to impersonate another particular person. The advantage of a mask is that it can be made from special materials, making it almost impervious to damage and allowing repeated, long-term use. The disadvantage is that some stiffness in the details is unavoidable. Making it convincing enough is much harder than with the first method."
"But this one doesn't look stiff." Pei Ye looked down at it.
"Yes. Making a mask this lifelike, capturing both form and spirit, takes a master's skill," Li Piaoqing said. "And the wearer's own face has to be suitable enough, too."
By then, the blade the girl had inserted had separated the skin. She steadily lifted the mask, exposing the corpse's true face. Pei Ye leaned over to look, and both of them froze.
A horrifying, uncanny visage lay beneath the mask. The girl now knew why this face was so suitable: it had no contours of its own at all.
The eyes, nose, and mouth remained, but the eyelids, bridge of the nose, and lips were gone.
They had not been sliced away. Instead, everything was smooth and even, looking entirely natural from birth. Almost any human-skin face could be laid over it without the slightest mismatch.
The face was truly uncanny and revolting. After only a few glances, the girl laid the skin back over it.
A shuddering chill rose in Pei Ye's heart