A soldier poses with a Hythe Mk III Gun Camera during training activities at Ellington Field, Houston, Texas in April of 1918. The Mk III, built to match the size, handling, and weight of a Lewis Gun, was used to train aerial gunners, recording a photograph when the trigger was pulled, for later review, when an instructor could coach trainees on better aiming strategies. (Photo by Harry Kidd/WWI Army Signal Corps Photograph Collection via The Atlantic)

Robert Price of TREWGrip LLC demonstrates a TREWGrip handheld rear-type keyboard and air mouse for Apple and Android tablets at the “CES: Unveiled”, media preview for International CES, at the Mandalay Bay Convention Center in Las Vegas on January 5, 2014. (Photo by Robyn Beck/AFP Photo)

Dark clouds bearing down on the city on April 17, 2011 in Foshan, Guangdong Province of China. According to flood control authorities on Monday, gales as strong as 45.5 meters per second, accompanied by hailstorm, cloudburst and strong wind battered cities including Guangzhou, Foshan, Zhaoqing and Dongguan of south China's Guangdong Province on Sunday, has killed at least 17 people and injured 118. (Photo by ChinaFotoPress/Getty Images)

“Contrails (short for “condensation trails”) or vapour trails are artificial clouds that are the visible trails of condensed water vapour made by the exhaust of aircraft engines. As the hot exhaust gases cool in the surrounding air they may precipitate a cloud of microscopic water droplets or, if the air is cold enough, tiny ice crystals”. – Wikipedia

Photo: An airplane leaves a vapor trail as it flies in front of he moon on January 17, 2007 above Hanover, Germany. (Photo by Alexander Hassenstein/Getty Images)

Impala pictured in the Kruger National Park on December 7, 2007 in Mpumalanga, South Africa. (Photo by Warren Little/Getty Images)

Mary McHugh mourns her slain fiance Sgt. James Regan at “Section 60” of the Arlington National Cemetery May 27, 2007. Regan, a US Army Ranger, was killed by an IED explosion in Iraq. (Photo by John Moore/Getty Images)

A wounded member of the Afghan police reaction force waits for treatment in Alingar, Laghman province, on April 30, 2012. A bomb exploded next to opium poppy fields during a poppy eradication campaign in, wounding two Afghan policemen, police officials said. (AP Photo/Rahmat Gul)

Thomas Thwaites of the United Kingdom accepts the 2016 Ig Nobel Prize in Biology for “creating prosthetic extensions of his limbs that allowed him to move in the manner of, and spend time roaming the hills in the company of, goats” during the 26th First Annual Ig Nobel Prize ceremony at Harvard University in Cambridge, Massachusetts, U.S. September 22, 2016. (Photo by Brian Snyder/Reuters)