Reverse engineering Chinese censorship

When and why are controversial tweets deleted?:
"For his final project, Tschang built on data collected on thousands of deleted weibos in China to look for answers. “We know that certain topics are censored from blogs hosted in China, Chinese search engines and Weibos,” Tschang writes in his paper. “But we don’t know where the line lies. Part of the reason is because the line is constantly moving.”"
I have always been fascinated by the Chinese firewall. Besides, the recent bumbling attempts to censor the Indian Internet have made this sort of topic worth attention again.