Chinese companies are outsourcing the censorship burden to third parties. The constant reviewing and blocking of content has to be done by humans; algorithms wouldn’t be able to catch everything.

These “professional censors” — before they can start spending their days taking content down — have to be introduced to China’s forbidden history (think of the 1989 Tiananmen Square crackdown):

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.

The whole environment is quite dystopic:

The screen saver on each computer is the same: photos and names of current and past members of the Politburo Standing Committee, the Communist Party’s top leadership. Workers must memorize those faces: Only government-owned websites and specially approved political blogs — a group on what’s called a whitelist — are allowed to post photos of top leaders.