Certain phrases
Here are some phrases that you will never be able to find in China: personality cult, I oppose, disagree, animal farm, and emperor. It may seem like a bunch of random words and sentences to you, but they have been used in the past to start protests and civil unrest in China.
Hence why they were all banned, but we are sure that new words and phrases have appeared in their place, after all, how many different ways can you express opposition? There are many different symbols and words that could be used, like we said before, censorship is a hard thing to stay on top of.