As the Chinese saying goes, a single spark can start a prairie fire.
What began as a row between a primary school teacher and a few policemen at the way officers were handling a dispute has escalated into a political movement that has sharply divided the city.
Nearly 3,000 people with opposing views took to the street on Sunday to express their anger. The half-day stand-off degenerated into a brawl at one point.
Some analysts warn that social tensions are running so high that any incident, if not handled properly, could trigger a political firestorm. Others fear free speech may be under threat.
It all started with a five-minute-34 second video clip that went viral. It shows Alpais Lam Wai-sze, a teacher at Pui Ling School of the Precious Blood in Fanling, losing her temper and shouting abuse at police handling a dispute in the pedestrian-only zone in Mong Kok.
Despite officers' efforts to calm her, Lam - who with her husband had trespassed onto a cordoned-off police area - jabbed her finger at a policewoman and shouted abusive language at her. She also abused other officers and used foul language.
Lam, whose father is a member of the radical League of Social Democrats, has declined to apologise to the police, although she has said sorry to her school, pupils and parents.
The July 14 incident was largely unknown to the public until eight days later when a video clip was posted on YouTube. Lam's identity was quickly revealed.
On July 26, her school apologised and admitted her act was improper. In the following days, police unions and civil servants' groups also condemned her.
Then a longer version of the video was posted, showing that the officers being abused were handling a dispute between rival groups - the Youth Care Association and the Falun Gong - over their use of space to hold a rally.
Youth Care is widely regarded as a pro-Beijing group, while Falun Gong is outlawed on the mainland but tolerated in Hong Kong. In the longer video Lam is seen accusing police of not handling the dispute fairly.
Now the saga has taken on a new dimension, turning into a confrontation between pro-Beijing and pro-democracy camps.
Lam's supporters, including some pan-democrats, praised the teacher for her bravery, while her critics said she set a bad example for young people.
Veteran China-watcher Johnny Lau Yui-siu said the focus should have been on whether the police had abused their power in handling the dispute.
"Some groups are overlooking the focus of the debate and keep on pursuing endlessly and irrationally the manner of an individual," said Lau, "The argument is empty. But it can easily … lead the public away from real, rational debate."
Lau warned that further confrontations could occur unless the government can balance the interests of rival sides.
Dr Cheung Chor-yung of City University's department of public policy said: "Free speech in Hong Kong seems at risk. The present situation seems to be that if you do not agree with me, you will be regarded as my enemy."
Dr Chung Kim-wah of Polytechnic University was pessimistic about any short term solutions. "The incident has in a sense been hijacked and has become a fight between the pro-government and pro-democracy camps. Either side would make the most of the dispute."