An Andalusian horsewoman waits for the animal to drink water before a classical dressage contest during the Sacab Andalusian Horse Show in Coin, southern Spain, April 12, 2015. (Photo by Jon Nazca/Reuters)

A robot Ecce by the Robot studio is pictured at the world's largest industrial technology fair, the Hannover Messe, in Hanover April 13, 2015. (Photo by Wolfgang Rattay/Reuters)

Madison Chock and Evan Bates of the U.S. compete during the ice dance short dance program at the ISU World Team Trophy in Figure Skating in Tokyo April 16, 2015. (Photo by Yuya Shino/Reuters)

School girls stand next to a ballot box at a polling station during the municipal elections in Havana April 19, 2015. Cuba held its first local elections since a historic thaw in relations with the United States with an unusual wrinkle in the single-party system: two of the 27,000 candidates openly oppose the government. (Photo by Reuters/Stringer)

Boeing B-29 (#10) from the 24th Bomb Squadron, 6th Bomb Group after an emergency landing at Iwo Jima on April 24,1945. (Photo by U.S. Air Force)

In this Thursday, April 11, 2013 photo, an Afghan woman peers through the the eye slit of her burqa as she waits to try on a new burqa in shop in the old town of Kabul, Afghanistan. (Photo by Anja Niedringhaus/AP Photo)

People at a Czech Stop look at a cloud of smoke rising from the explosion in West, Texas, April 17, 2013. (Photo by Andy Bartee via Dallas Morning News/MCT)

A girl allows a butterfly to be placed on her nose at the Sensational Butterflies exhibition at the Natural History Museum on April 6, 2011 in London, England. The exhibition is divided up into five sensory zones exploring how butterflies see, hear, taste, smell and touch. The display containing hundreds of butterflies runs from April 12 to September 11, 2011. (Photo by Peter Macdiarmid/Getty Images)