. "One of those tortured died three months down the line.
"They were using iron bars, they were using logs, hitting us. One would be pinning you, one was stepping on the neck. One would be holding the legs and then the other one beating you on the buttocks using an iron bar."
Today, Dr Zhou is more concerned about the signals sent out by the European Union's decision in February to ease sanctions against his country. He fears that the plight of Zimbabwe and its teachers, under the regime of 90-year-old president Robert Mugabe, has been forgotten.
"The international world seems to have abandoned Zimbabwe," he says. "We are deemed to be a post-conflict country, yet we are in conflict."
The teacher, who has also worked as an academic, traces Zimbabwe's problems back to the 1990s. By the end of that decade, Dr Zhou and his colleagues had been prompted to form the country's only independent teaching union.
It has not been easy. Beatings and torture aside, the PTUZ has also had to fight to be allowed to exist, and suffers from the government unilaterally deregistering its members - who, like all public servants, are banned from collective bargaining - and taking their subscription money. Meanwhile, its leaders face constant surveillance.
"They come during the night and you don't know what they want," says Dr Zhou, in England as a guest of the NASUWT union. "They come in a car with no number plates."
But his union's difficulties only reflect the wider troubles experienced by Zimbabwe's teachers. According to Dr Zhou, 75,000 of them left the profession between 2000 and 2008.
"No teacher in Zimbabwe would want his child to train as a teacher or to be married to a teacher," he explains. "If any mother knows that you are in love with a teacher [she will say] `Why are you doing this to me?' "
Money is a particular problem, with teachers paid as little as pound;146 a month, although wages do not always arrive. The result, Dr Zhou says, is poverty for teachers who are "always selling bananas and sweets in order to augment their salaries".
Now his union says the situation could get even worse. Last week it warned that it would fight a government plan to stop paying teachers during school holidays.
All this is part of a deliberate strategy by the Mugabe regime, Dr Zhou believes. "Politicians are aware that as a teacher we are so powerful. We have so much influence but they have realised that the voice of the poor man is never respected. So it is by design."
Problems are compounded by promotions based on political affiliation rather than merit, and teachers are forced to teach a "national patriotic studies" syllabus that the union says amounts to propaganda and an "invasion of professional space".
"Someone can simply walk into a school and say, `This teacher is not a good teacher. I want this teacher to be dismissed,' " Dr Zhou says. "A teacher that was good suddenly becomes bad."
He says that things become particularly difficult during election times, when students are taught "certain military skills" and told to "spy over their teachers".
"There are youth militia that move from school to school asking teachers which political party they belong to," he adds. "Teachers become bitterly afraid of their students. We have lost the dignity and the laughter."
Dr Zhou says the country has remained in "election mode" after national polls in July 2013 that were widely condemned as fraudulent. He still lives in Zimbabwe, despite being accused of being an "academic terrorist" by the authorities, and admits he does not always feel safe.
But he adds: "I must not fear what happens to me. I must continue to talk because I have lost everything."