Like a scene out of a Hong Kong triad movie, the mahjong parlour in Temple Street is filled with cigarette smoke, the incessant click-clack of tiles and the grim, hard faces of gamblers.
On a prominent altar for Guan Gong, the righteous Taoist God of War, lies a giant bundle of ginger, shaped like a hand. A knife is stabbed through it - an ominous warning, it seems, for anyone contemplating cheating at the tables.
The manager of Hong Kong's oldest mahjong parlour Kai Kee Mahjong laughs it off. "It's just to create sat hei, a menacing atmosphere, which brings good fortune to our business," says Mr Devil Yau - his real name, he insists.
Filled with mystique, rituals and superstitions - including the famous one about wearing red underwear for luck - playing mahjong has long been a way of life for Hong Kongers.
And it has been posited that the game is a possible factor for why they are among the longest-living people in the world. Last year, the city's men and women came in second in terms of longevity after Japan, living to ages 81 and 86.3 respectively.
Various studies have documented the health benefits of mahjong, due to the need for a player to calculate points and remember the rules and tiles already thrown out, as well as for its social interactivity. Three or four players are needed to form a table for a game.
In a study published this year, the Hong Kong Institute of Education found that regular mahjong playing and taiji practice among nursing home residents slow down cognitive decline even for those suffering from dementia, as compared with those engaged in handicraft activities.
"Mahjong kept them mentally active through participation in a leisure activity that is enjoyable and mood-lifting," says Professor Cheng Sheung Tak, a psychology and gerontology academic who led the research.
It is, thus, not surprising that the game is finding new life here in a different form: as therapy for elderly patients in hospitals and nursing homes.
The Yan Chai Hospital Nursing Home in Tsuen Wan, for one, introduced "mahjong therapy" in 2004. Today, 60 of its 300 residents undergo the programme.
Every resident is accompanied by an aide, who tailors the help according to his or her needs. For instance, the focus for those suffering from Alzheimer's disease will be to help them regain physical agility in their arms, by rearranging and throwing out tiles. Those who are more mentally sharp will be guided to think through how they will play the game.
Since then, the effects have been clear, says occupational therapist Tse Wai Ho, citing an elderly woman suffering from mild Alzheimer's disease who used to keep shouting and could not concentrate on any particular activity. "During the game, she stayed quiet, and after three months, she stopped shouting even when she was not playing mahjong."
The programme has also become popular among the residents, he says. "They look forward to it and you can heard them reminding one another that today or tomorrow is Mahjong Day."
But away from nursing homes and hospitals, the game's own longevity appears at stake.
While the sound of swirling mahjong tiles and muttered Cantonese oaths at a weak hand continues to resonate, in homes, at the back of shops and even some wedding banquets, the game purportedly invented by Confucius in 500BC appears to be falling out of favour.
In particular, mahjong parlours - with a whiff of disrepute about them as dens of iniquity, with rough characters, shady transactions and brawls - report dwindling business.
Today, there are just 66 licensed mahjong parlours in the city - fewer than half of the 144 established in 1956 when the colonial government started licensing what it termed "mahjong schools" to avoid appearing to condone gambling.
A visit to five clustered in Kowloon's working-class districts of Yau Ma Tei and Jordan shows that most players are in their 40s to 60s.
"Young people rarely come," says Mr Yuen Wai, manager at Shui Hing Mahjong in Portland Street. "They would rather play computer games at home."
But hardy establishments are finding ways to survive.
They are now reaching out to people from China, where mahjong parlours are illegal.
For instance, many of them now abide by Shenzhen-style rules, instead of the Hong Kong or Cantonese style. Instructions are also often rendered in simplified Chinese script - as used in the mainland - instead of the traditional characters customary in Hong Kong.
"About 30 per cent of our customers are now from the mainland," says Mr Gordan Lam, 68 a grandson of Mr Lam Kwan who opened Kai Kee in 1930 - initially as a provisions store, later adding mahjong tables to draw customers. The space with about 20 tables draws around HK$100,000 (S$16,000) in commissions a month, he says.
For now, players like housewife Mimi Fung, 46, are keeping them afloat. She began playing mahjong at 14 - and has been hooked since.
Trying to sum up its charm, she says: "Mahjong is not only a game, it is like real life. You can tell a person's personality from the way he plays mahjong."
Additional reporting by Pearl Liu