A person who died more than a thousand years ago is still intact, uncorrupted, and not reduced to bones; this is simply an inconceivable existence.
"Sister, this person has become a host for a vengeful spirit," Xiao Sui said directly.
"Oh?" Xiao Yao asked curiously, "Is that the reason for his body not decaying?"
"Not exactly. It's after rotting that the vengeple spirit reshaped its body," Xiao Sui replied. "A vengeful spirit is just an aggregation of countless strands of resentment. Its true form is a mass of black Qi, but it's suppressed by the Buddha statues in the tomb and can't escape. It can only rely on this body to leave. After a millennium of cultivation, it has become almost human. However, looking at it now, if we had come later, it might truly have become a demonic being, appearing in the human realm and becoming a calamity," Xiao Sui explained the nature of such evil spirits as if it was common knowledge.
Indeed, demonic beings exist! But then again, it makes sense.