Chongqing KTV refuses unprintable songs

Resently in Chongqing, KTV has been introduced a new monitoring system to prevent people singing obscene songs.

As the official says, this system is complusory but free to enstall. Once someone request a prohibated songs, the light will shine and then the system will automatically call the police.

But there is one little question: why will a prohibated song appear in the menu? And how do they judge whether a song is obscene or not?