Wherever large numbers of people have congregated, rats have also made their homes. In London and New York it has frequently been remarked that no one is ever more than a few metres away from a silently lurking rodent. And in warm, densely built-up places such as Hong Kong, it is easy for vermin to survive and proliferate: food left in open places, uncovered rubbish bins and gutters and drains all encourage the grey, long-tailed urban rat.

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Scientific advances throughout the 19th century, particularly discoveries and developments in microbiology, made the links between public filth, vermin such as rats and outbreaks of epidemic disease abundantly clear.

From the time the Chadwick Report into public sanitation was published, in 1882, exposing the dire state of public cleanliness in Hong Kong and consequent risk to civic health and well being, the importance of adequately dealing with the city’s rodent nuisance has been apparent. The bubonic plague, which first appeared in Hong Kong in the spring of 1894 and continued to return, due to inadequate sanitation, until the late 1920s, was spread by rat-borne fleas.

Cleansing measures were heavily subsidised by the government – because they had to be. In pre-scientific times, most ordinary Chinese people made little or no connection between the condi­tions they and their ancestors lived in and the diseases that were visited upon them.

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Epidemic diseases – as everyone knew – were caused by malevolent ghosts and curses put about by evil-wishers, not unseen microbes. Ritual observances such as periodic fire dragon festivals were regarded as sufficient to deal with any outbreak of disease.

Inevitably, people had to be offered cash rewards to act in the common good – appeals that extend beyond one’s individual bene­fit are seldom adequate motivation. Cash bounties were offered for trapped rats – or the tail of a rat, which was considered sufficient proof of the creature’s demise – that were brought to police sta­tions. In the pre-war years, these bounties led to well-organised smuggling operations whereby rats were brought in from the main­land specifically to be handed in for the reward. From time to time these scams would be rumbled and the perpe­trators prosecuted.

Black, pungent Jeyes Fluid – popularly known as “chow shui” (stinky water) – was given out free of charge for disinfectant purposes. Much like carbolic soaps of the same era, Jeyes Fluid and its instantly recognisable, coal-tar smell have now largely vanished. Along with other “threatened” sights and sounds, this once-characteristic local odour could, perhaps, be added to one of Hong Kong’s various lists of endangered intangible cultural-heritage assets.

Across Hong Kong, markers for the city’s long years of decline into near-complete political paralysis and dysfunction since the 1997 handover can be observed. Illegal parking in Central is blind-eyed by officials allegedly responsible for enforcement, planning regulations are flouted with impunity right across the New Territories, air pollution remains a major problem – the sorry list of official inaction goes wearily on. While the sluggish cats meant to patrol this society have been otherwise distracted and co-opted, Hong Kong’s metaphorical rats have run riot.

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Fortunately, the real ones continue to be firmly dealt with. Rat collection has remained a top official priority; Hong Kong’s Urban Services Department maintains a 24-hour hotline dedicated to the immediate removal of captured rodents. Ring them up, at whatever hour, and a team will be swiftly dispatched to remove the offending critter for scientific examination, humane execution and hygienic disposal. Like much else that appears anachronistic in Hong Kong, this situation is somehow endearing.