A murmuration of migrating starlings is seen across the sky in southern Israel December 31, 2015. (Photo by Amir Cohen/Reuters)

This picture taken on January 25, 2015 shows a participant taking part in an ice water challenge in Zhangjiajie, central China's Hunan province. Participants were required to stay in an ice pond, holding an ice block while eating ice-cream with an electric fan blowing at them. (Photo by AFP Photo/Stringer)

Piper Hoppe, 10, from Minnetonka, Minnesota, holds a sign at the doorway of River Bluff Dental clinic in protest against the killing of a famous lion in Zimbabwe, in Bloomington, Minnesota July 29, 2015. A Zimbabwean court on Wednesday charged a professional local hunter Theo Bronkhorst with failing to prevent an American from unlawfully killing “Cecil”, the southern African country's best-known lion. The American, Walter James Palmer, a Minnesota dentist who paid $50,000 to kill the lion, has left Zimbabwe. He says he did kill the animal but believed the hunt was legal and that the necessary permits had been issued. (Photo by Eric Miller/Reuters)

Francis Sierra, 23, smokes as she competes for the longest ash during the XVIII Habanos Festival in Havana, March 3, 2016. (Photo by Alexandre Meneghini/Reuters)

A devotee is smeared with a vermillion powder while celebrating the “Sindoor Jatra” vermillion powder festival at Thimi, in Bhaktapur, Nepal, April 14, 2016. Devotees mark the festival by playing traditional drums, singing, dancing and carrying chariot of various deities around town while throwing vermillion powder to welcome the advent of spring and the New Year. (Photo by Navesh Chitrakar/Reuters)

A couple who did not give their names walk in downtown Havana, February 2, 2015. (Photo by Alexandre Meneghini/Reuters)

Disguised participants strike poses on a car during the ancient carnival of Ituren, in the northern Spanish Navarra province on January 30, 2017. The yearly three day festivities, revolving mainly around agriculture and principally sheep hearding, run on the last Sunday, Monday and Tuesday of January where Navarra Valley locals from two villages dress up and participate in a variety of activites as they perform a pilgrimage through each village. (Photo by Ander Gillenea/AFP Photo)

Demonstrators help a fellow protester during clashes with security forces during an opposition rally in Caracas, Venezuela on April 4, 2017. Protesters clashed with police in Venezuela Tuesday as the opposition mobilized against moves to tighten President Nicolas Maduro' s grip on power. Protesters hurled stones at riot police who fired tear gas as they blocked the demonstrators from advancing through central Caracas, where pro- government activists were also planning to march. (Photo by Carlos Garcia Rawlins/Reuters)