Participants ride horses, hold spears and wear historic armoured suits of the Middle Ages as they compete during the Saint George international knight tournament in Moscow, Russia, May 3, 2015. (Photo by Maxim Zmeyev/Reuters)

A Sri Lankan leopard is pictured at a zoo in Dehiwala near Colombo on March 3, 2016, on World Wildlife Day. (Photo by Ishara S. Kodikara/AFP Photo)

Mud-covered tourists pretend to be trapped inside a mud prison at the Daecheon Beach Mud Plaza in the city of Boryeong on South Korea's west coast, July 17, as they take part in the Boryeong Mud Festival, which opened that day and runs through July 26. Boryeong mud is rich in natural mineral component and is considered to prevent skin aging. (Photo by EPA/Yonhap)

Men ride on a “mikoshi” or portable shrine as local people carry it into the sea during a festival to wish peace in the ocean and good fortune in the new year in Oiso, west of Tokyo, January 1, 2015. (Photo by Yuya Shino/Reuters)

Children wave Vietnamese and American flags while waiting for arrival of U.S. President Barack Obama (not pictured) before a welcoming ceremony at the Presidential Palace in Hanoi, Vietnam May 23, 2016. (Photo by Reuters/Kham)

A man jumps over a puddle outside Victoria Station, as heavy rain falls, in London, Monday June 20, 2016. Monday marks the Summer Solstice – the longest day of the year and the astronomical change of seasons when days are longest and nights are shortest in the Northern Hemisphere. (Photo by Lauren Hurley/PA Wire via AP Photo)

Sara Moni, dressed as the World of Warcraft's Sinestra, poses for photographers on day three of the Comic-Con International held at the San Diego Convention Center Saturday July 23, 2016 in San Diego. (Photo by Denis Poroy/Invision/AP Photo)

Sara White, dressed as Ginny Weasley, a fictional character in J. K. Rowling's Harry Potter series, poses for portrait at the launch of “Harry Potter and the Cursed Child” at Foyles book store on July 30, 2016 in London, England. The script book of the play of the same name, which is on at Palace Theatre, billed as the eighth Harry Potter story, is on sale from midnight tonight. (Photo by Rob Stothard/Getty Images)