Censorship is probably as old as language itself. Okay, maybe it’s not that old, but there were censorship laws in Ancient Greece and in Dynastic China more than 2,000 years ago. From the Latin verb censere meaning “to appraise, value or judge,” the word “censor” was first used to name the Roman official who oversaw public morals.

How censorship is implemented, though, shifts over time. Today, book burning has given way to internet firewalls and deleted content.

Last year, Facebook and Twitter played large roles in connecting the protestors of the Arab Spring and in broadcasting their message to the international community. The internet certainly has the potential to play a role in protests and anti-government movements. However, the web, by its nature, is searchable and can also be used by governments to find and stymie anti-government efforts.

From the outside, the choices of censors can seem bizarre. Take for example, the situation in China. China is notorious for its internet censorship, and government censors regularly delete posts on blogs and social media. Twitter and Facebook are completely disabled. Jokingly called “the Great Firewall,” the Chinese censorship department automatically flags undesirable content, and then human censors read each post and choose whether or not to delete it.

Recently, a group of graduate students at Carnegie Mellon University conducted a long-term project on what words are flagged by internet censors in China. They traced the likelihood that a post would be deleted if it contained certain words. Most words that attracted the attention of censors were predictable: Tiananmen Square, Tibet, Falun Gong. Other words really surprised the researchers. Polynices (the mythical son of Oedipus who supposedly encouraged anarchism) raises the eyebrows the censors. Most surprisingly iodized salt is flagged. Why salt? After the Fukushima earthquake, rumors spread around China that iodized salt could protect someone from radiation poisoning. In order to quell that rumor, the Chinese government has been directly censoring it.

Chinese citizens evade the censors with clever methods. They often use slang or homophones instead of directly addressing something. Also, they use Romanized letters (like English), which are not flagged by the search engines. Most clever of all, they sometimes use images of text instead of text itself. Images are not searchable on the web; they show up as blank space, unless you directly tag them with a description. So, you can write something, take a picture of it, and post the picture – completely under the radar.

What do you think of these flagged words?