There's a move in figure skating which competitors have not been allowed to attempt on the ice since 1976 because it's seen as so dangerous.
That hasn't stopped people from attempting them on the odd occasion but it does tend to lead them being slapped with a penalty for trying something they know they shouldn't do.
This banned move is of course the backflip, as you might have seen pulled off to a stunning degree of skill in the video above.
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While it's clearly not impossible it is still incredibly dangerous and thus illegal to attempt for those who enjoy strapping blades to the bottom of their shoes and gliding about on a large mass of ice.
There are plenty of good reasons why it's not really allowed to be done, even if it does look undeniably cool when pulled off.
Doing a backflip on a surface of hard ice is pretty obviously a hazardous activity, especially since ice skaters don't load up on protective gear to take the worst of the potential impacts.
On top of the risk, the move itself is just considered to be not that aesthetically pleasing in the sport so it wouldn't win much favour with the judges even it wasn't illegal.
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Basically any jump where your legs go over your head is a huge no-no lest there be some almighty and painful crack of the skull, neck or some other important part of the body occurring when you land back down on the ground.
There are also concerns that a potentially heavy landing with the person's entire weight slamming down onto one blade could mess up the ice surface for the next competitor.
While it's illegal and can get a skater into trouble there have been people who pull it off anyway to show they are good enough to do it.
One of the most famous examples is from the video above where French skater Surya Bonaly successfully performed a backflip and landed on one foot, all on an ice skate while in motion.
Whichever way you slice it that's a seriously impressive athletic achievement, being able to backflip right over and land near-perfectly on one thin blade of metal skittering across an icy surface.
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In the moment you can view above Bonaly pulls off the backflip and lands on one blade, and she is the only Olympic figure skater who has managed to pull off this feat, though she had her score docked when she did it at the 1998 Nagano Winter Olympics.
Other athletes have done backflips on ice but they land them with both feet on the ice and skating jumps are meant to be landed with one foot.