US Michael Phelps celebrates winning the men's 4x200-metre freestyle relay at the 2016 Rio Olympics by biting his medal. Photo / AP
They're not made of chocolate, but that doesn't stop a huge number of Olympians biting their medals when posing for photos.
The very fact they're posing for photos could be the reason why.
David Wallechinsky, president of the International Society of Olympic Historians, told CNN that cash-hungry snappers were probably telling the Olympic champs what to do.
"It's become an obsession with the photographers," says Wallechinsky, co-author of The Complete Book of the Olympics.
"I think they look at it as an iconic shot, as something that you can probably sell. I don't think it's something the athletes would probably do on their own."
The practice of biting into metal seems to have its roots in counterfeiting, CNN said.
Money handlers bit coins to test their authenticity - gold is relatively soft and shows wear easily.
This year's Olympic medals are only about 1.34 per cent gold. They're mostly silver (93 per cent) with the rest copper, CNN added.
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