Even with the highest medical skill, to diagnose a poison, one must at least know what the poison is.
Clearly, Ye Huan knew about the Purgatory Soul-Eater poison!
"I always thought I was the only person in the world who knew how to brew Purgatory Soul-Eater. I never expected Emperor Wu could brew it too. Is his mastery of medicine really that high?" Ye Huan asked.
Chapter 302