A woman takes part in a four-minute flash mob pillow fight at the Old Town Square in Prague, Czech Republic, December 22, 2016. (Photo by David W. Cerny/Reuters)

Flash, a golden retriever, plays with a toy following a press event for the American Kennel Club to reveal the nations most popular dog breeds in the Manhattan borough of New York, February 22, 2016. (Photo by Carlo Allegri/Reuters)

Female of pygmy hippopotamus called Malaya from Netherlands in zoo in Dvur Kralove nad Labem, Czech Republic, February 22, 2016. (Photo by David Tanecek/CTK via ZUMA Press)

An empty cell block is pictured within Joint Task Force Guantanamo's Camp VI at the U.S. Naval Base in Guantanamo Bay, Cuba March 22, 2016. (Photo by Lucas Jackson/Reuters)

Cowboy Alexis Azeituno, 25, from Guatemala, gets ready to ride a bull during the International Livestock Fair Show in Havana March 22, 2015. (Photo by Alexandre Meneghini/Reuters)

Erica Bougard of the U.S. competes in the high jump event of the women's heptathlon during the 15th IAAF World Championships at the National Stadium in Beijing, China, August 22, 2015. (Photo by Fabrizio Bensch/Reuters)

Women, wearing traditional “ao dai” dress, pose for a photo next to peach blossom flowers ahead of Vietnamese “Tet” (the lunar new year festival) in a field in Hanoi January 22, 2017. (Photo by Reuters/Kham)

Pope Francis attends a circus performance during his weekly general audience at Paul VI hall on December 22, 2016 at the Vatican. (Photo by Alberto Pizzoli/AFP Photo)