"Side Effect" 

"The gas reacts with caffeine? What do you mean?" Lai Jiayi furrowed her eyebrows and slowly sat down on the couch again. 

"I think the dramatic gas effect should only make the victim overreact, quack, like what you did, " Yaya started to explain while still hovering in the air. 

"B-but in Zhao Yang's case, quack, he drank coffee. The gas might react with the caffeine inside the coffee, quack...and…" 

Yaya gulped. He took a deep breath and continued. "It might give out a side effect, showing the victim's new side that's 180° different from their real character, quack!" 

...hm?? 

Lai Jiayi gaped. The girl looked at Yaya with wide eyes. 

'The explanation matches! At first, Zhao Yang is only overreacting, but as time passes by, he shows a side that's 180° different from his real self!'