Wrap your arm around your back, then, with the same arm, reach in front and touch your belly button. Done? Congratulations, you have a tiny waist (or tentacles for arms). Post a picture online and enjoy your bragging rights.
Over the past week, the "belly button challenge" has exploded onto social media in China. Millions of - mostly female - netizens have posted self-portraits of themselves attempting it.
Asian celebrities have jumped on the bandwagon, including South Korean singer Sehun of popular K-pop boyband Exo.
The belly button challenge has also reportedly become the No. 1 trending topic on Weibo - China's answer to Twitter - gathering more than 130 million hits in just two days.
The viral trend is believed to have stemmed from Chinese actress Yang Mi's selfie, posted last week.
Accompanying the picture of the 28-year-old actress is a caption in Chinese that roughly translates as: "Reverse- arm touching belly button means that I have a good figure. Praise me."
In Singapore, the trend has yet to catch on, although a handful of people, such as Channel 8 actress Sora Ma (@soramayx), have shared photos of themselves doing it on Instagram.
Celebrities SundayLife! spoke to say they are aware of the challenge, having seen posts about it on Weibo and Instagram. When SundayLife! hit the streets to ask people to attempt it, most said they had found out about it on social media.
While it appears to be nothing more than harmless fun, the challenge has been criticised in the Western media for sending out negative messages about body image.
The Huffington Post's Marci Warhaft-Nadler wrote: "What scares me is the fact that a lot of people don't realise just how dangerous these fads can be for anyone battling an eating disorder."
James Hamblin of American magazine The Atlantic wrote an article titled Don't Try The Belly Button Challenge, arguing that it is linked to "body shame and dangerous culture glorifying disordered eating, which is a social disease".
A survey of selfies posted on Weibo reveals that most individuals successful in the challenge are widely complimented. Those who fail, however, are mocked and told to hit the gym and lose flab.
A 24-year-old woman from the city of Chongqing tried so hard to succeed that she dislocated her shoulder in the process, reported the Beijing Morning Post last weekend.
But does the belly button challenge really act as a good indicator of a svelte body? Not so, says yoga and pilates instructor Dawn Sim, 35.
Flexibility, as opposed to fitness levels, is the key to success here, she explains.
"Some people will find this easier to do compared with others because they have more flexibility around their shoulders, elbows and wrists, and this is not an indicator of fitness.
"Even an athlete in great shape can have difficulty attempting this because the bone structure around their shoulder joints can inhibit movements at certain angles.
"On the other hand, a sedentary individual born with hyper mobile joints can achieve this with very little effort," says Ms Sim, who is five months pregnant with her fourth child and can do the challenge with ease.
So it would seem that people should treat this belly button challenge as just a bit of fun and not take it too seriously.
Ms Jolene Tan, programmes and communications senior manager at Aware (Association Of Women For Action And Research), says: "There's obviously no harm in trying a quirky pose or picture for fun, but it shouldn't become a way of scrutinising women's bodies for whether they are 'good enough'."
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Additional reporting by Samantha Goh
"I do body stretches every morning so it's not too hard for me. Warm up before this practice, to avoid muscle cramps."
SORA MA, 31, Channel 8 actress
"I think this is as far as my hand can go."
TOSH ZHANG, 26, actor and rapper
"I am winded from these moves."
CHUA ENLAI, 36, comedian and actor
"I'm actually quite happy that I can't do it. I think as a guy, I don't pride myself on having a slim waist. I'd rather have a healthy and sturdy physique."
DARRYL YONG, 30, actor
"A perk of being skinny: You can do this easily."
NOAH YAP, 22, YouTuber and Ah Boys To Men (2012) actor
"If only my belly button were 3 inches to the right."
HARESH TILANI, 31, comedian and YouTuber (YouTube Channel: MinistryOfFunnyTV)
"I'm actually more flexible than I thought, that's surprising!"
WANG WEILIANG, 28, actor-host
"I think younger kids can do it more easily than the adults. This is so hard!"
MS LINDA HILL (left), 44, housewife, with her children, Shobi Hill (centre), seven, and Bailey Hill, 12
"I can barely get my hand around my back, let alone touch the belly button. It's tough!"
MS BINA VARMA (centre), 41, banker, with her friends
"It's impossible for me. How do they do it?"
WU TONG (left), 19, student, with XIAO SIYUE, 18, student
"You need to stretch a lot to be flexible, but it still takes a lot of effort to pull it off!"
SHARLYN SEET, 14, student
"I think you need practice to get it right. Otherwise, there's no way you can ever reach it."
MUHAMMAD SOLLEHIN, 17, student
PHOTOS: SAMANTHA GOH, COURTESY OF CHUA ENLAI, SORA MA, CHUA ENLAI, DARRYL YONG, NOAH YAP, HARESH TILANI
