A man poses for a picture to show his rings of gold, silver and bronze on his fist in Zamfara, Nigeria April 21, 2016. (Photo by Afolabi Sotunde/Reuters)

Palestinian bedouin shepherds pull their lambs into the water to wash them, in Gaza City, on April 29, 2016. Every year before the beginning of the summer, shepherds wash their herds in the sea. (Photo by Mohammed Abed/AFP Photo)

A massive sand storm cloud is close to enveloping a military camp as it rolls over Al Asad, Iraq, April 27, 2005. (Photo by Cpl. Alicia M. Garcia, U.S. Marine Corps/Reuters/U.S. Department of Defense)

Spanish bullfighter Julian Lopez “El Juli” adjusts his montera (bullfighter's hat) before starting a bullfight at the Malagueta bullring in Malaga, southern Spain, April 4, 2015. (Photo by Jon Nazca/Reuters)

A professional bull rider participates in a bull riding exhibition at the premiere of “The Longest Ride” at the TCL Chinese Theatre on Monday, April 6, 2015, in Los Angeles. (Photo by Chris Pizzello/Invision/AP Photo)

Period-costumed actors participate in the 150th anniversary re-enactment of the surrender of General Robert E. Lee to General Ulysses S. Grant at the Museum of Confederacy in Appomattox, Virginia, April 9, 2015. (Photo by Jay Paul/Reuters)

A comedic photo of a cheetah appearing to find something hilarious by Dutton Robert for the Comedy Wildlife Photo Awards 2016, South Africa, April, 2012. (Photo by Dutton Robert/Barcroft Images/Comedy Wildlife Photo Awards)

A roadside ice-cream vendor waits for customers at a market in New Delhi, India, April 7, 2016. The Indian economy is characterized by the existence of a vast majority of informal or unorganized labor employment. (Photo by Altaf Qadri/AP Photo)