A masked Burundian protester faces soldiers in front of a burning barricade during an anti-government demonstration against President Pierre Nkurunziza's bid for a third term in the capital Bujumbura, Burundi, 25 May 2015. Street protests continued on 25 May as the United Nations Secretary-General Ban Ki-moon condemned the killing of the leader of the oppsition party Union for Peace and Development (UPD) Zedi Feruzi who opposed Nkurunziza's bid. (Photo by Dai Kurokawa/EPA)

People dressed as zombies take part in a “Zombie Walk” parade in Athens, Greece, February 25, 2017. (Photo by Michalis Karagiannis/Reuters)

Italian Air Force's aerobatic demonstration team, the Frecce Tricolori leave colourful vapour trails as they fly over the Altare della Patria monument on Republic Day (Festa della Repubblica) in Rome, Italy, 02 Jun 2017. The anniversary marks the founding of the Italian Republic in 1946. (Photo by Massimo Percossi/EPA)

Men slide in the mud during the Boryeong Mud Festival at Daecheon Beach in Boryeong, South Korea, Saturday, July 22, 2017. The 20th annual mud festival features mud wrestling and mud sliding. (Photo by Ahn Young-joon/AP Photo)

American actress and singer Bella Thorne attends the GQ Mexico Men of The Year Awards 2017 on October 26, 2017 in Mexico City, Mexico. (Photo by Victor Chavez/Getty Images)

Gold medalists Kikkan Randall and Jessica Diggins of the United States dancing during the medal ceremony for Cross-Country Skiing – Ladies' Team Sprint Free on day 13 of the PyeongChang 2018 Winter Olympic Games at Medal Plaza on February 22, 2018 in Pyeongchang-gun, South Korea. (Photo by Eric Gaillard/Reuters)

Two men dressed as the Statue of Liberty look for tourists to pose with them for pictures in exchange for donations in New York's Times Square on January 20, 2015. (Photo by Jewel Samad/AFP Photo)

This Thursday, January 22, 2015 photo made with a long exposure shows the glow from a Noctiluca scintillans algal bloom along the seashore in Hong Kong. The luminescence, also called Sea Sparkle, is triggered by farm pollution that can be devastating to marine life and local fisheries, according to University of Georgia oceanographer Samantha Joye. Noctiluca itself does not produce neurotoxins like other similar organisms do. But its role as both prey and predator tends can eventually magnify the accumulation of toxins in the food chain, according to R. Eugene Turner at Louisiana State University. (Photo by Kin Cheung/AP Photo)