After they had restrained Chen Hui, Miao Qing made another move and successfully hypnotized him. The truth quickly emerged, just as Qin Hai had suspected: Chen Hui, that kid, was indeed the mastermind behind putting the substandard materials into the production containers.
After being bribed, this kid and another worker from the workshop had done the deed together. The three workers on shift on the 22nd were none the wiser. Even the reason Liu Sihai and Li Jian had diarrhea was because Chen Hui had put laxatives in their breakfast that morning. Yan Kuan did not exhibit any symptoms because he had not eaten in the company cafeteria that morning.
Once the hypnosis was over, Qin Hai played the recording of the session for Wan Qiang. The latter immediately flew into a rage, stormed into the office, and gave the sleeping Chen Hui a vicious beating. If Qin Hai hadn't intervened in time, Chen Hui might have actually been beaten to death by Wan Qiang.