Militants loyal to Yemen's exiled government ride on the back of a pick-up truck in the country's central city of Taiz August 19, 2015. Militia forces loyal to Yemen's exiled government fought their way deep into the central city of Taiz this week, local officials said, largely pushing out Houthi militiamen from the country's third largest city. (Photo by Reuters/Stringer)

A man in “Red Army” garb hits the pavement during a simulated attack during a re-staging of part of the Long March in Jinggangshan September 14, 2017. The scene brings alive an extraordinary chapter in China's history that established the supremacy of Chairman Mao Zedong and the Communist Party. Deep in the mountains of Jinggangshan in the southeastern province of Jiangxi, a classroom of bank tellers participates in an ideological boot camp that plays into Chinese President Xi Jinping's drive to further consolidate his grip on power. (Photo by Thomas Peter/Reuters)

A man carries a block of ice left behind by a hailstorm in Sao Paulo, Brazil, on May 19, 2014. After the severe overnight hailstorm a layer of hailstones as deep as 20 centimeters covered streets and parks, drawing people to make snowmen and play in the ice, an unusual scene to the city. (Photo by Nelson Antoine/AP Photo)

Dinara Safina of Russia hits a backhand in her match against Arantxa Parra Santonja of Spain during the BNP Paribas Open at the Indian Wells Tennis Garden on March 10, 2011 in Indian Wells, California.

Caroline Wozniacki of Denmark serves to Alisa Kleybanova of Russia during the BNP Paribas Open at the Indian Wells Tennis Garden on March 15, 2011 in Indian Wells, California. (Photo by Matthew Stockman/Getty Images)

A competitor prepares to snorkle during the World Bog Snorkelling Championships on August 28, 2011 in Llanwrtyd Wells, Wales. In 2012, following the Olympic Games, Llanwrtyd Wells will host the inaugural World Alternative Games. (Photo by Harry Engels/Getty Images)

A patient buried in the hot sand looks out from under a shade that protects his face from the sun in Siwa, Egypt, August 12, 2015. In the searing heat of summer in western Egypt, at the hottest time of the day, sufferers of rheumatism, joint pain, infertility or impotence lie buried neck-deep in the sand of Siwa near Dakrour Mountain. Locals say taking a sand bath is a natural therapy with powers to cure many medical conditions. (Photo by Asmaa Waguih/Reuters)

Dani tribeswoman smokes a cigarette and shows her amputated fingers in, Western New Guinea, Indonesia, August 2016. Deep in the highlands of Western New Guinea, Indonesia, lives one of the world’s most isolated tribes. Known as the Dani people, the tribe was unwittingly discovered by American philanthropist, Richard Archbold, after an expedition in 1938. (Photo by Teh Han Lin/Barcroft Images)