Weird Game: Only I See Through the Rules

Six people, a pure white doorless secret room. The rules are simple: ninety minutes of discussion each round, with two people voted to be executed until the end of the game. Before the first round of voting, I stared at the corpse in the corner - it was left over from the previous game. The others panicked, but I laughed. I have played this game. They thought it was a random death draw. Su Qing, a female white-collar worker, is forming a gang, Zhao Gang, a middle-aged man, smashes the wall angrily, Lin Wei, a female doctor, gently comforts everyone, Liu Yu, a college student, hides in the corner and trembles, and Wang Jianguo, a retired police officer, tries to use logic to deduce the truth. Only I know - that person who is shivering may be just faking it. Only I know - two must die in each round, but the undercover agent can change his vote. Only I know - the real rules of this game are hidden in the unspoken corners of the system. I didn't tell them. Because what I want to see is who will reveal the flaws. In the second round of voting, I smiled and pointed to an unexpected person: "Liu Yu, stop pretending. Your trembling rhythm doesn't match your breathing rate." She raised her head and her eyes suddenly became sharp: "How do you know?" How do I know? Because in the last round of the game, I was killed by her. This time, I want the undercover to vote with his own hands and vote himself out.