Undercover? Why undercover? What's the special meaning?

The popularity of the Hong Kong film Infernal Affairs in 2003 made its title synonymous with undercover.

"Undercover": It is another name for a policeman who has been sneaking into criminal gangs for a long time. This is a special police set up by the police station to help solve difficult cases or major cases. At present, there are more than 80 "undercover" in the Hong Kong Police Force lurking in various criminal groups. The "undercover" police must be voluntary, not only children, but also innocent for three generations; "Undercover" is generally recruited by the society or trainee police, and the face must be unfamiliar. "Undercover" has many special rights. It can "fake the truth", be promoted quickly after retirement, and enjoy the treatment of living abroad. Kind of like the federal government.

Note: Gangs sometimes have undercover in police stations. Undercover is not suitable for the police.

The following is a vivid joke about undercover:

Rice and steamed bread fight in groups, and rice depends on many people. When you see the wrapped ones, you hit them. No one is spared, such as bean paste buns, sugar buns and steamed dumplings. Steamed dumplings were cornered, so they pulled their clothes and shouted, look, it's plain clothes!