After reaching a certain stage of evolution, players from the Eastern District may experience mental illness. It's said that this happens because certain parts of their brains mutate collectively during evolution. They may not be aware of it, but mutant plants might be affected, so it's better to carry them along to manage the condition.
This theory could hold, given the various directions evolution can take. Others might believe it, but since it involves Doctor Zhang and the Eastern District players, who have mental issues, it's hard for Xu Huo to believe this is just Yuquan City's genetic mutation.
