A rare spiritual artifact used to test whether one's body has been possessed by another soul. It is the size of a sparrow's egg, translucent with swirling white mist inside. When possession is detected, the mist turns blood-red, symbolizing the karmic bond between possessor and possessed. It defies logic and cannot be deceived even by immortals. It is Dayu's greatest treasure, enshrined in the ancestral temple. Old Wang brought it to test Yu Sangsang, but it showed no red mist, confirming she had not been possessed.
