Before Mo Lei'er made her move, she yelled, "See the sword coming!"
To be honest, Mo Lei'er didn't know why she yelled. And she was extremely unwilling to do so.
It's a sneak attack, yet I actually shouted to remind the enemy to guard before making a move? What logic is this?
Just before her move, Mo Tianji had instructed her multiple times — "Before making a move, you must be perfectly invisible. But when you make the move, you must yell!"
This sentence, Mo Tianji had repeated it over and over for several times!
Later when Mo Lei'er was annoyed by it and finally agreed, Mo Tianji still reiterated it one more time.
Mo Lei'er almost lost herself under complete inability to comprehend.
So before she attacked, Mo Lei'er reluctantly yelled.
This yell was really a big deal!
She was originally in a state of complete invisibility, and such invisibility couldn't hide Xiao Chenlei's perception!