Hmph, that explains it. So this old woman is an Evil Spirit!
When Lin Fei saw the old woman surnamed Wu, his Spirit-Observing Divine Eye immediately revealed her true nature as an Evil Spirit.
The Evil Spirit race is a form of soul-based life that takes possession of human bodies and lives among people in human guise. They possess extremely potent concealment abilities, making it impossible for a cultivator's Soul Sense to detect their presence. The only way they give themselves away is by using the unique Runic Art of the Evil Spirit race.
Chapter 425