Turkana tribesmen walk with guns in order to protect their cattle from rival Pokot and Sambur tribesmen near Baragoy, Kenya February 14, 2017. Cattle rustling and competition for grazing have long troubled northern Kenya, but severe drought and political rivalries ahead of the elections have exacerbated the situation between ethnic tribes. (Photo by Goran Tomasevic/Reuters)

A hippopotamus is sprayed with water on a hot summer day at Anna National Zoological Park in Chennai, India on April 26, 2017. (Photo by Arun Sankar/AFP Photo)

Journalists walk through the corridor of the stopped third reactor at the Chernobyl nuclear power plant in Chernobyl, Ukraine April 20, 2018. (Photo by Gleb Garanich/Reuters)

Londoners sleep on the platform and on the train tracks at Aldwych Underground station,London, during heavy all night Nazi bombing raids, October 8, 1940. (Photo by AP Photo)

A zoo employee carries three-month-old female giant panda cub, born to mother Liang Liang and father Xing Xing, on display to the public for the first time at the national zoo in Kuala Lumpur, Malaysia, November 17, 2015. (Photo by Olivia Harris/Reuters)

Devil Ark manager Dean Reid reacts as Tasmanian Devil joeys climb on him before the first shipment of healthy and genetically diverse devils to the island state of Tasmania leave the Devil Ark sanctuary in Barrington Tops on Australia's mainland, November 17, 2015. The largest group so far of disease-free Tasmanian devils has been released in the wild, as part of plans to save the carnivorous marsupials from a cancer threatening them with extinction. (Photo by Jason Reed/Reuters)

Pakistani street performers sit around fire waiting for customers on a chilly evening in Rawalpindi, Pakistan, Wednesday, November 11, 2015. Some parts of Pakistan are facing a harsh winter. (Photo by B. K. Bangash/AP Photo)

The original costumes for Star Wars character Darth Vader stand on display at “Star Wars: The Exhibition” at County hall on May 04, 2007 in London, England. (Photo by MJ Kim/Getty Images)