A competitor solves a Rubik's cube using his feet as he prepares for the Rubik's Cube European Championship in Prague, Czech Republic, July 15, 2016. (Photo by David W. Cerny/Reuters)

A Mai-Mai rebel soldier shows off his guns at a checkpoint near the Mugunga refugee camp in Zaire; 1996. (Photo by Carol Guzy/The Washington Post)

An engineer begins the process of conducting a block-by-block inspection of the exterior of the Washington Monument while suspended by ropes September 27, 2011 in Washington, DC. The National Park Service has closed the landmark in the nation's capital indefinitely due to damage caused by a 5.8 magnitude earthquake in August. (Photo by Win McNamee/Getty Images)

Tibetan monks create an intricate picture made from coloured sand at St. Mungo Museum of Religious Life and Art on November 23, 2011 in Glasgow, Scotland. The monks, from the Panchen Lama's Monastery, are creating a Sand Mandala as part of a Tantric Buddhist ritual, invoking the presence of the Buddha in a design representing the palace of the deities. (Photo by Jeff J Mitchell/Getty Images)

The Brooklyn Bridge is seen after a crane pulled by a tug boat on the East River slammed into scaffolding beneath the Bridge on March 13, 2012 in New York, NY. According to reports, no damage was done to the structure of the bridge. (Photo by Allison Joyce/Getty Images)

Space shuttle Atlantis launches from pad 39A on July 8, 2011 at the NASA Kennedy Space Center in Cape Canaveral, Florida. The launch of Atlantis, STS-135, is the final flight of the shuttle program, a 12-day mission to the International Space Station. (Photo by Bill Ingalls/NASA via Getty Images)

The hull on a boat that carried Rohingya migrants for three months is seen at Langkawi island, in the Malaysia's northern state of Kedah, Malaysia, May 12, 2015. Thailand and Malaysia may set up camps and detention centers to shelter hundreds of refugees arriving on their shores, officials said on Tuesday, as a leading inter-governmental agency said about 7,000 boat people were still adrift in the Bay of Bengal. (Photo by Olivia Harris/Reuters)

A People's Liberation Army (PLA) commando jumps through a fire hoop part of an exercise during an open day event at the Ngong Shuen Chau Barracks, the PLA navy base in the territory, in Hong Kong, China, 01 July 2015. Thousands of visitors attended the PLA open day yesterday and today to mark the 16th anniversary of the handover from British rule. (Photo by Jerome Favre/EPA)