In the busy, polluted city of Mumbai in India, it's sometimes hard to find the time to smile.
Rickshaws — local yellow and black open cabs — clog the streets night and day.
Roads and public places display the sad view of desperate families living in shacks, very young children begging, and men who call themselves holy men, stalking tourists and locals for a fistful of rupees.
But every morning, a group of older folks escapes the smokes and horns of Mumbai's streets to gather at a park in the Mumbai suburbs.
They are followers of laughter yoga, a therapy that blends yoga-like stretching with laughing.
Most of them — pensioners — like to begin their day together.
They clap and they breathe, until they laugh like children, forgetting for an hour the hardships of Mumbai's busy life.
"If we remain in the house," said 60-year-old Meera Tellan, "we think of our household problems. But when we come here, we forget all our worries. We forget our depression."
"It's a therapy," said Nagaradj Hair, 59. "We feel better and we feel young. What else do you want? This is the [best] thing, which you get [for] free! No charge!"
Today, laughter yoga is a global movement, with 5,000 clubs in Asia, America and Europe.
Local Indian clubs are free, but disciples from rich countries are ready to spend lofty amounts of money to be with the master.
This spring, the movement's founder, Madan Kataria, a Mumbai physician, is holding a rock star-like global tour in Hong Kong, Tokyo and Switzerland.
For $1,200, Kataria's followers will be able to spend a week in Switzerland to laugh with him.
Kataria has also taken the joys of stretching and laughing to the corporate world.
"People are killing themselves with stress in the work place," said Kataria.
He said he recently worked with an Indian automobile company, which will incorporate laughter yoga into its daily routine.
A therapy applied to individuals and professionals, school children and elderly people, laughter yoga is a success story of our times, and its evolution started in a small Mumbai park 12 years ago.
One early morning in 1995, Kataria was writing an article about the physical and mental benefits of laughter.
"Suddenly, I get a flash in my mind," recalled Kataria. "Why not start a laughter club?"
On the same day, Kataria gathered a few friends and shared jokes with them. But very quickly, "We ran out of jokes."
"Sexy, negative jokes came in, that was not funny," he said. "So, then I found this idea of laughing for no reason."
Kataria argues that children can laugh 400 times a day — compared to grown-ups, who laugh less than 15 times — because children laugh for no reason, without using sophisticated forms of humor.
Laughter yoga sessions feature a special kind of laugh — a mechanical laugh — which, when performed with other people, becomes genuine laughter.
Every morning, members of the local Mumbai club, which ABC News visited, practice the Namaste laughter, or Greeting laughter, in which followers hold their hands as in prayer. And there's also the Lion laughter — hands open around their face and tongues out — and the Lassi laughter (a local dairy drink) in which disciples mimic drinking an imaginary cup filled with laughter — the more they drink, the more they laugh.
Their mechanical laughs may seem a bit odd, almost disturbing to the non-initiated.
And even at the park that morning, not all were convinced.
Children witnessed the session, laughing awkwardly, and busy adults passed by, staring suspiciously at the twelve folks who were extending their tongues and laughing.
But laughter yoga has greatly helped some people in despair, like 80-year-old Somoti, who said she had lost the use of her legs before joining laughter club.
Today, she is back on her feet and enjoys the company every morning. That has given Somoti a good reason to smile.