A Syrian boy looks through a gate as others wait to cross into Syria at Oncupinar border crossing in the southeastern city of Kilis, Turkey February 11, 2016.. (Photo by Osman Orsal/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)

U.S. Marines, left, and South Korean Marines, wearing blue headbands on their helmets, take positions after landing on the beach during the joint military combined amphibious exercise, called Ssangyong, part of the Key Resolve and Foal Eagle military exercises, in Pohang, South Korea, Saturday, March 12, 2016. North Korea said Saturday its military is ready to pre-emptively attack and “liberate” the South in its latest outburst against the annual joint military drills by the United States and South Korea. (Photo by Kim Jun-bum/Yonhap via AP Photo)

A Mark IV tank, part of the parade at the Lord Mayor's Show in London. (Photo by Topical Press Agency/Getty Images). November 1917

Models promote a condom brand at the first Shenzhen s*x Culture Festival on September 21, 2007 in Shenzhen of Guangdong Province, China. The festival aims to increase awareness about reproductive health and popularise s*x education. (Photo by China Photos/Getty Images)

Nora Muaid stands in Zawraa Park on December 2, 2011 in Baghdad, Iraq. The park's 180-foot tall Ferris wheel opened earlier this year and is the second largest in the Middle East. (Photo by Mario Tama/Getty Images)

A general view of Edinburgh Castle on February 7, 2012 in Edinburgh, Scotland. The castle dominates the city skyline was built on top of an extinct volcano, and has had a human settlement on the castle site since 900BC. (Photo by Jeff J. Mitchell/Getty Images)

“Show Time”. It's a normal behavior of mantis. They're doing defence. When they're afraid of; raising their arms and spreading their wings. They looks like smiling dancer. Photo location: Nicosia, Cyprus. (Photo and caption by Hasan Baglar/National Geographic Photo Contest)