One evening a couple of weeks ago, a short, bearded man walked into a lecture theatre at the University of Hong Kong. The room was packed and people were sitting on the steps and standing against the walls. The talk was sponsored by the architecture department, but many people in the audience were there because of their interest not in architecture but in something else: politics.
That is because the speaker was Ai Weiwei , China's most prominent artist, designer, architect, iconoclast and, in the eyes of the central government, a leading troublemaker.
Ai was put under house arrest in Beijing on Friday to stop him from going to Shanghai, where a huge outdoor crab party to 'celebrate' the ordered demolition of his new studio was held on Sunday, with hundreds braving official displeasure to attend.
In his Hong Kong talk, he detailed among other things the bizarre Shanghai events. First of all, it seems, the Shanghai authorities invited him two years ago to put up a building there to house his studio.
But then - with no explanation and the huge red-brick and concrete building just completed - they asked him to demolish it on the grounds that it was an illegal structure.
Ai suspects that officials were offended by his political activities, some of which were directed at the Shanghai government, such as a documentary he made on a Shanghai activist who spent three months at Narita airport in Tokyo because Chinese officials refused to let him back in.
Ai's father, Ai Qing, was a renowned poet and an ardent communist. In fact, he changed his name to Ai because he did not want to have the same surname as Chiang Kai-shek, the Kuomintang leader. Despite his position in the party, the poet was purged during the anti-rightist campaign of 1957 and exiled to Xinjiang for 20 years. 'Every day I saw my father cleaning toilets,' Ai said. 'When I grew up I thought a poet was someone who cleaned toilets.'
His father wrote about his love for China's landscape but Ai today finds it meaningless.
'The poems can be used by real estate developers to promote their projects,' he said. 'They own all the land in China today.'
Ai is not sure whether his father, who died in 1996, would approve of his political activities. But, as he made clear, he has to live his own life.
Indeed, when asked what he thought of nationalism, Ai responded that there were not many words that he took exception to, but nationalism was one of them. He found the very concept repulsive.
Perhaps because the party is keenly aware of the harsh treatment meted out to Ai Qing, his son has managed to stay out of prison. Ai is also protected, in a sense, by his international status.
His achievements, after all, include being co-designer of the 'Bird's Nest' stadium for the Beijing Olympics. He now has an exhibition at London's Tate Modern.
But he is better known for his political activities. After the Sichuan earthquake in 2008, he was outraged that so many children perished when badly constructed schoolhouses collapsed. He went on a campaign to find out how many children had died and what their names were.
But the government would not co-operate. In the end, Ai and others made a list of earthquake victims by knocking on doors and asking about the children who had died. And, he said, the government responded by treating these names as state secrets.
Why didn't the authorities want Ai to go to Shanghai? Because he was planning a feast of river crabs to mark the demise of his studio, his way of making fun of the authorities.
The word for river crabs is hexie, which sounds the same as the word for harmony, a virtue constantly extolled by the Communist Party. By giving a crab party, Ai was poking his finger in the eyes of the communist authorities.
And that, it is clear, was something that they could not accept.
Frank Ching is a Hong Kong-based writer and commentator