A zookeeper feeds a hippopotamus with a watermelon in its enclosure in Belgrade's zoo, Serbia, July 20, 2015. Temperatures in Serbia have risen up to 40 degrees Celsius (104 degrees Fahrenheit), according to official meteorological data. (Photo by Marko Djurica/Reuters)

Vietnamese female commissioned officers of the signal force march during a parade marking their 70th National Day at Ba Dinh square in Hanoi, Vietnam September 2, 2015. (Photo by Reuters/Kham)

Visitors watch as members of a local winter swimmers club pour buckets of cold water over their daughters, 7-year-old Liza Broverman and 2-year-old Alisa Smagina during a celebration of Polar Bear Day at the Royev Ruchey zoo, with the air temperature at about minus 5 degrees Celsius (23 degrees Fahrenheit), in Krasnoyarsk, Russia, November 27, 2016. (Photo by Ilya Naymushin/Reuters)

Catholic faithfuls hold figurines of baby Jesus during a religious procession on Holy Innocents Day in Antiguo Cuscatlan, El Salvador, December 28, 2016. (Photo by Jose Cabezas/Reuters)

An Iraqi woman attends a festival commemorating the International Day of Peace in Baghdad, September 21, 2015. (Photo by Thaier al-Sudani/Reuters)

2016 Rio Olympics, Weightlifting, Final, Women's 63kg, Riocentro, Pavilion 2, Rio de Janeiro, Brazil on August 9, 2016. Marina Rodriguez (CUB) of Cuba competes. (Photo by Stoyan Nenov/Reuters)

Netherland's Kitty van Male is hit in the face by Argentina's Agustina Habif during the women's quarterfinal field hockey game, August 15, 2016. (Photo by Carl de Souza/AFP Photo)

2016 Rio Olympics, Rhythmic Gymnastics, Final, Individual All-Around Final, Rotation 1, Rio Olympic Arena, Rio de Janeiro, Brazil on August 20, 2016. Melitina Staniouta (BLR) of Belarus competes using the hoop. (Photo by Ruben Sprich/Reuters)