What does it mean to accidentally kill two mice and cats?

In the film, the police are given two identities, namely "cat" and "mouse", and two of them are metaphors of the police. For the first time, the police chief sent a special police officer to drill into the ventilation duct, and showed the eyes of the mouse and the special police officer with symmetrical pictures, suggesting that the police were equal to the mouse and became "rats" who succumbed to powerful people.

The other is what Lin Rilang asked afterwards: "Are you a cat or a mouse?" The original clear answer implied that the little people questioned the power. The police, as the privileged personnel of the state who enforce the law impartially, should be the cats who enforce justice (in line with the name of police Zhang Zhengyi played by Yam Tat-wah). However, when they serve the powerful, they become "rats" walking in the dark, and their dual identities are constantly switched according to the plot. Lin Rilang can only use public opinion and morality as threats in an attempt to find light in the cracks.