The New York Times has an article about China's online censorship factories [nytimes.com] and how they operate. Censors are specially educated accurately in history and politics so that they have mastery over how to spot and eliminate references, even indirect ones, to forbidden topics. Potential employees fro censorship factories have to cram for two weeks for a comprehensive exam which they must pass in order to begin work. This education is followed by ongoing training which includes regularly visiting and reviewing web sites normally blocked by the Great Firewall of China.
Li Chengzhi had a lot to learn when he first got a job as a professional censor.
Like many young people in China, the 24-year-old recent college graduate knew little about the 1989 Tiananmen Square crackdown. He had never heard of China’s most famous dissident, Liu Xiaobo, the Nobel Peace Prize laureate who died in custody two years ago.
Now, after training, he knows what to look for — and what to block. He spends his hours scanning online content on behalf of Chinese media companies looking for anything that will provoke the government’s wrath. He knows how to spot code words that obliquely refer to Chinese leaders and scandals, or the memes that touch on subjects the Chinese government doesn’t want people to read about.
Earlier on SN:
Censorship a Trojan Horse [soylentnews.org] (2018)
Unpublished Chinese Censorship Document Reveals Effort to Eradicate Online Political Content [soylentnews.org] (2018)
The "Great Cannon" of China [soylentnews.org] (2015)