The mainland-based Douban website touts itself as a movie database but a search for Hu Jie's 2007 documentary Though I Am Gone - about the brutal killing of a school principal during the Cultural Revolution - proves fruitless.
The mainland may have sanctioned other films which broach the so-called '10 years of catastrophe' but Hu's film is still banned because of its subject.
The victim at the centre of the film, Bian Zhongyun, was vice-principal of the Experimental High School attached to Beijing Normal University, a prestigious institution which, during the Cultural Revolution counted among its students - and thus, its Red Guards - the descendants of the country's highest-ranking leaders.
Even without the political complications, Though I Am Gone - challenges the authorities anyway, given Hu's account of Bian's fate. (It is screening on August 4 at the Film Culture Centre as part of documentary-making collective Visible Record's Moon Beam showcase).
Bian, among the first intellectuals to fall foul of the Maoist extremists, was dragged into the school playground, drenched in black paint, and clubbed to death on August 5, 1966. Though I Am Gone, driven by her husband Wang Qingyao's memories and photographs, is the sad story of an individual who died in a time of inhumanity. The couple had four children.
Wang recalls asking his wife to leave her post to avoid the political storm about to hit her school. She refused, saying she was innocent of any wrongdoing. Days later, she was killed by her own students, described by a colleague as having transformed into jackboot-wearing fanatics within a few days of Mao Zedong's call for revolution.
'They were laughing - and laughing at whom?' Bian's co-worker Lin Mang asks. It's a question that's relevant today in a country where dissident voices can still be silenced at will.
Though I Am Gone, Aug 4, 2.30pm, Film Culture Centre, Flat A3, 11/F Tung Nam Factory Building, 40 Ma Tau Kok Rd, To Kwa Wan. Free admission