There was some Harry Potter-level Dark Magic during swimming events this weekend at the Olympics: As competing backstrokers periodically emerged from the surface of Rio de Janeiro’s Aquatic Stadium pool, fans were aghast at they saw the terrifying visage of Voldemort himself, flat-faced and slick, repeatedly bobbing out of the water. Has the Dark Lord mistaken the Olympics for the reemergence of the long-dormant Triwizard Cup Tournament?

Fear not, Cedric Diggorys of the swimming community: What viewers mistook for the third coming of He Who Shall Not Be Named was merely a quirk of water’s chemistry, albeit one that’s scary as hell. Because of the way H2O molecules fit together at the atomic level, the water acts like a heavy sheet as the swimmers surface. Pulled taut over their features as they approach the water’s edge, the weight of the sheet pulls their faces into that characteristic snakelike sneer.

Failed Olympian Lord Voldemort would be a better swimmer if he had a nose.
Failed Olympian Lord Voldemort would be a better swimmer if he had a nose.

The way water maintains surface tension is, in a sense, magical: Water doesn’t seem to follow the standard rules of physics, which is why water forms droplets and water striders can walk, Jesus-style, on a pond’s surface. What’s happening on the surface of the pool as the faux-Voldemorts emerge for air is that the individual water molecules are straining to stay together. On the atomic level, the negatively charged oxygen-containing half of one water molecule is attempting to maintain ties to the positively charged hydrogens on another one. When this interaction happens between the trillions of water molecules in a pool, water acts like a single, face-smashing layer.

Of course, even water’s extraordinary bonds aren’t strong enough to contend with the force of a rapidly moving Olympian. As the swimmers break the surface tension of the water, our visions of the Dark Lord dissipate, only to form again the next time the submerged faces come up for air.

Muggles checking the skies above the Aquatics Stadium for a Dark Mark can relax — for now.

Photos via Getty Images / Al Bello, Getty Images / Clive Rose

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.