A number of Olympians - including the most decorated Olympic athlete of all time, Michael Phelps - have been photographed with large red circles on their skin.
What are they, and why is everyone suddenly going dotty over them?
The mark of an Olympic athlete, at least at Rio 2016, seems to be a scattering of perfectly round bruises. Swimmers and gymnasts, particularly from Team USA, are among those seen sporting the mysterious dots.
No, not paintballing misadventures or love bites - they are the result of a practice known as "cupping"; an ancient therapy where heated cups are placed on the skin.
So how is 'cupping' done?
The technique, which is a form of acupuncture, is done by lighting flammable liquid in a glass cup.
Once the flame goes out, the drop in temperature creates suction which sticks the cups to the body.
The suction pulls the skin away from the body and promotes blood flow - and leaves those red spots, which typically last for three or four days.
Why are some Olympians using it?
Athletes say they are using it to ease aches and pains, and to help with recovery from the physical toil of constant training and competing.
There are plenty of other recovery techniques competitors use - including sports massage, sauna, ice baths and compression garments - but US gymnast Alex Naddour told USA Today that cupping was "better than any money I've spent on anything else".
"That's been the secret that I have had through this year that keeps me healthy," Naddour told the paper, adding that it had saved him from "a lot of pain".
His team captain Chris Brooks added that many on the squad had started "do-it-yourself" cupping, with cups that can be suctioned with a pump rather than with a flame.
"You're like, 'OK, I'm sore here,'" said Brooks. "Throw a cup on, and your roommate will help you or you can do it yourself."
The marks visible on Michael Phelps as he competed in the men's 4x100m freestyle relay on Sunday had people on social media speculating what they might be, with some guessing he might have been playing paintball or attacked by a giant octopus.
Who else does this?
It's not only athletes who use cupping. The practice has long proved popular among A-listers in search of the next best therapy.
In 2004, Gwyneth Paltrow appeared at a film premiere revealing the signs of cupping on her back.
Justin Bieber, Victoria Beckham and Jennifer Aniston have all been photographed with what look like cupping marks.
And Nicole Richie made her dad, singer Lionel Richie try it - although pictures suggest he might not entirely have enjoyed it.
Cupping has also become an increasingly available and popular treatment in beauty parlours and spas, as well as traditional Chinese medicine shops where it is commonly on offer.
Doesn't it hurt?
The British Acupuncture Council (BAcC) says cupping is not painful, and the red marks left on the skin are caused by blood being drawn to the surface and small capillaries rupturing.
On the other hand, swimmer Michael Phelps was filmed wincing as he underwent the technique in a recent advert, and other Olympians have posted pictures of what look like painful cupping sessions on social media.
US swimmer Natalie Coughlin posted a picture of cups suctioned to her chest - with the words: "Laughing because it hurts so bad" - and a painful looking pictureof the aftermath of the therapy.
Belarusian swimmer Pavel Sankovich also posted a photo of his legs covered in a dozen of the little domes.
esearchers also looked at the theory that a drop in physical activity was the main reason for rising weight gain.
But they say if a reduction in exercise was solely responsible, every single adult nationally would need to have eliminated more than three-and-a-half hours of daily walking since the 1970s to account for the changes.
They suggest policymakers trying to curb obesity should focus more on reducing calorie intake than promoting exercise.
Public health expert Prof Alan Maryon-Davis described the report as an "interesting and very soundly argued analysis".
He added: "This will send a shudder through the junk-food industry.
"Up until now they've been able to point to what was thought to be a decline in the nation's calorie intake and say there's really no need for tougher measures like a sugar tax, fat tax or calorie-labelling on alcoholic drinks.
"But this latest analysis rather pulls the rug from under their feet."
The Behavioural Insights Team, which is jointly owned by the UK government and charity Nesta, applies insights from academic research in behavioural economics and psychology to public policy and services. BBC