Two women jump into a frozen pond as they compete in the Polar Plunge at Frozen Dead Guy Days in Nederland, Colorado March 14, 2015. The winter festival in the small mountain town commemorates the 1994 discovery of the corpse of Bredo Morstol, which is now housed in a shed on dry ice above the town. (Photo by Rick Wilking/Reuters)

Zahra Lari runs in a scene shot for the Nike Middle East ad campaign filmed in Dubai, UAE, February 10, 2017. An online commercial released by Nike (NKE.N) this week that showed Arab women fencing, boxing and spinning on ice-skates has stirred controversy over its attempt to smash stereotypes about women leading home-bound lives in the conservative region. (Photo by Reuters/Nike)

Lisa Yu crawls through a mud pit under low slung barbed wire as she competes in The Tough Bloke Challenge on March 4, 2012 in Melbourne, Australia. The Tough Bloke Challenge is one of the most gruelling adventure runs in Australia consisting of 18 obstacles over a 6 km cross-country course laden with thick mud-pits and ice-cold water crossings. (Photo by Scott Barbour/Getty Images)

“The Challenge!” Young boy relishes in a game of tug of war before school. Photo location: Lake Titicaca, Peru. (Photo and caption by Paul Heyman/National Geographic Photo Contest)

A polar bear plays with a pylon during celebrations marking its first birthday in an enclosure at Tierpark Hellabrunn zoo in Munich December 9, 2014. (Photo by Michaela Rehle/Reuters)

This undated handout photo received from the Antarctic Ocean Alliance on October 28, 2016 shows a adelie penguin jumping onto the ice in the Ross Sea in Antarctica. The world's largest marine reserve aimed at protecting the pristine wilderness of Antarctica will be created after a “momentous” agreement was finally reached on October 28, 2016 with Russia dropping its long-held opposition. (Photo by John Weller/AFP Photo/Antarctic Ocean Alliance)

A goose has terrorized students at the University of Warwick, Coventry, UK, on May 22, 2013. The bird built its nest near a block of student apartments and attacks anyone who goes near the nest. (Photo by Caters News/The Grosby Group)

Iraqi Kurdish female fighter Haseba Nauzad looks through a pair of binoculars during a deployment near the frontline of the fight against Islamic State militants in Nawaran near Mosul, Iraq, April 20, 2016. (Photo by Ahmed Jadallah/Reuters)