Because the bookshelves inside are all iron shelves.
There aren't many books on the iron shelves, only a dozen or so bamboo scrolls, making it look quite sparse.
Duan Yun picked up one of the scrolls and unfurled it.
"On the fifth day of the leap month, I entered the Netherworld, accidentally discovering a Divine Cave, filled with Goddesses, residing in the crystal..."
Duan Yun quickly confirmed that this was the Ghost Mother's journal.
He had killed so many martial arts experts, and he could basically deduce one thing, which is that there weren't many earnest individuals among them since more or less of them kept diaries, writing down their insights and feelings.
Sure enough, the Ghost Mother couldn't escape this habit either.
And it was through these diaries that Duan Yun could finally link the information about the Netherworld together.
It turned out that the place where he first saw the stored "brains" was indeed a factory.
