Iraqi soldiers work at a radio station at Makhmour base, Iraq April 17, 2016. The Iraqi army has set up a radio station at its base in Makhmour broadcasting into areas south of Mosul controlled by Islamic State militants. The radio, which reaches villages halfway to the northern city, broadcasts military anthems and messages to the more than one million civilians living there. Radio operators said their aim was to weaken the militants’ morale and reassure civilians that the military has not forgotten them after nearly two years under Islamic State control. (Photo by Ahmed Jadallah/Reuters)

A native Brazilian competes in a tora competition, which is a race while carrying a log, during the Indigenous Youth Games of Pataxos nation in Santa Cruz de Cabralia, Bahia state, Brazil, April 18, 2016. (Photo by Roosevelt Cassio/Reuters)

A containment shelter for the damaged fourth reactor (L) and the New Safe Confinement (NSC) structure (R) at the Chernobyl Nuclear Power Plant are seen from Ukraine's abandoned town of Pripyat, Ukraine, April 22, 2016. (Photo by Gleb Garanich/Reuters)

Ukrainian teenagers hit each other with pillows during a large pillow fight in downtown Kiev, Ukraine, 24 April 2016. About hundred people took part in the event “Pillow battle 2016” in Kiev. (Photo by Roman Pilipey/EPA)

A wildlife ranger strokes a northern white rhino, only three of its kind left in the world, ahead of the Giant Club Summit of African leaders and others on tackling poaching of elephants and rhinos, Ol Pejeta conservancy near the town of Nanyuki, Laikipia County, Kenya, April 28, 2016. (Photo by Siegfried Modola/Reuters)

An undated handout picture made available on 29 April 2016 by the Toronga Zoo shows a baby echidna making a remarkable recovery after being attacked by chickens in a family's backyard at the Taronga Zoo in Sydney, Australia. (Photo by EPA/Taronga Zoo)

Iraqi Kurdish female fighter Haseba Nauzad looks through a pair of binoculars during a deployment near the frontline of the fight against Islamic State militants in Nawaran near Mosul, Iraq, April 20, 2016. (Photo by Ahmed Jadallah/Reuters)

Alex Plunkett, left, and Sean Hart, both of Arlington, Va., join hundreds participating in the annual International Pillow Fight Day on April 5. Massive pillow fights broke out on the Mall in Washington and in cities around the world. (Photo by Marvin Joseph/The Washington Post)