... But then, how would that substance know to differentiate?

[That sounds way too magical even for Xie Lian. What kind of sorcery would be necessary for an inanimate substance like this to even be able to identify and discriminate between people, beast or plant, and then decide on what effect to have...]

Maybe it has to do with where it is found? The healing or invigorating effects seemed to happen more in the fields, with the plants. Weren't the bad effects more in the forest?