Amygdalin leaves and Black Sage Vine did not go together. Hence, it would leave a layer on the plank after wiping.
Even though the brush did not have any ink, it was made of snow wolf fur. Thus, it could easily leave marks on the plank. It was a rather simple method, but it would stump anyone who did not have an understanding of it.
The pair wanted to make things difficult for Chu Liuyue so that she would embarrass herself.
They were gloating when Chu Liuyue said that the item was not working, thinking that they had successfully played a trick on her. However, they could no longer laugh when they saw the words on the plank.
The smile on Cui Yao's face stiffened as his eyes filled with surprise, making him look rather odd.
Mo Liang was not any better. He realized what had happened almost instantly. Chu Liuyue did it on purpose! She knew exactly what to do but pretended not to know.