"So, you want us to investigate the alchemists on the blood clotting Island and see if there's anything wrong with them, right?" When Shen Nan heard Zhao Hai's words, he understood what Zhao Hai meant by asking him to do. Zhao Hai had asked him to investigate what was wrong with those alchemists. So this was the root cause.
Zhao Hai nodded. When he mentioned the combination of sorcery and poison, he was referring to the art of curses. However, he could not mention the art of curses because there was no concept of curses in the upper realm. Hence, he only mentioned the combination of sorcery and poison. This way, Shen Nanzheng and the rest would be able to understand it more.
