LONDON - JUNE 04: A piece entitled “Entrance into wood” by Elke Krystufek goes on show at The Royal Academy Summer Exhibition on June 4, 2008 in London. In it's 240th year, the exhibition displays a wide range of recent work by both established and emerging artists. 10,000 artists submitted work for selection this year. (Photo by Peter Macdiarmid/Getty Images)

Two chimpanzees share a piece of watermelon at Taronga Zoo on December 23, 2010 in Sydney, Australia. (Photo by Rick Stevens/Taronga Zoo via 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)

A jockey takes part in a traditional cattle race or “Pacu Jawi”, to mark the end of the rice harvest in Tanah Datar, West Sumatra, Indonesia, August 13, 2016 in this photo taken by Antara Foto. (Photo by Hafiz Mubarak A./Reuters/Antara Foto)

A customer buys a box of bullits and a target of Osama Bin Laden October 3, 2001 at Blue Ridge Arsenal in Chantilly, VA. Guns sales have risen across America since the September 11th terrorist attacks. (Photo by Mark Wilson/Getty Images)

A pornographer posing as a fashion photographer sets up a photoshoot with an unsuspecting model, in the hope of getting some illicit footage. He suggests she try wearing something a little more suggestive. (Photo by Pryor/Three Lions/Getty Images). Circa 1955

Two brown bear cubs born at Whipsnade Zoo. (Photo by Evening Standard/Getty Images). 1970