A sculptor walks past ice sculptures at the Snow and Ice Sculpture Festival “Eiswelt Mainz” in Mainz, Germany, November 22, 2016. (Photo by Ralph Orlowski/Reuters)

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)

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)

Minnie Mouse, left, and Katy Perry attend a ceremony honoring Minnie with a star on the Hollywood Walk of Fame on Monday, January 22, 2018, in Los Angeles. (Photo by Mario Anzuoni/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)

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)