In fact, shortly after Yan Ao boarded the Ghost Ship, he discovered Captain Rotting Beard's problem.
When he had previously left a mental mark on the captain, Yan Ao noticed that everyone on the Ghost Ship, including Captain Rotting Beard, had a faint trace of mental imprinting upon them.
At first, Yan Ao thought this was the blessing of the Hell Demon Sound that Xifaliv had mentioned.
Chapter 484