“Slow”. A calm cow in the messy streets of Jodhpur. Photo location: India. (Photo and caption by Matthias Troeger/National Geographic Photo Contest)

A giant new exhibition space created by famed graffiti artist Banksy opens to the public on May 3, 2008 in London, England. The disused tunnel beneath Waterloo station has been transformed by 30 artists from around the world. The three day event, tagged as the “Cans festival”, also invites the public to add their own stencil art. (Photo by Jim Dyson/Getty Images)

People watch as an acrobat rides his motorcycle around a circular track at an entertainment park set up outside a shrine in Rawalpindi, Pakistan, on June 19, 2013. (Photo by Muhammed Muheisen/Associated Press)

Wounded people walk after clashes with riot police in central Kiev February 18, 2014. Ukrainian riot police advanced on the heart of 12-week-old protests against President Viktor Yanukovich on Tuesday and security forces set a deadline to end disturbances after at least five protesters were reported killed in a day of clashes. (Photo by Vlad Sode/Reuters)

America in the 1970s: Texas. Motorcyclist loading his possessions onto a truck with the help of his friends in Leakey, May 1973. (Photo by Marc St. Gil/NARA via The Atlantic)

The British rock and roll group the Beatles talk to Ed Sullivan at CBS Studio 50 before their live television appearance on “The Ed Sullivan Show” in New York, February 10, 1964. From left to right are, Sullivan, John Lennon, Ringo Starr, holding a cigarette, and Paul McCartney. (Photo by AP Photo)

Elfyn Evans of Great Britain and Daniel Barritt of Great Britain compete in their M-Sport WRT Ford Fiesta RS WRC during Day One of the WRC Australia on September 11, 2015 in Coffs Harbour, Australia. (Photo by Massimo Bettiol/Getty Images)

A hot air balloon in tortoise shape flies in the air during the Tazaungdaing air balloon festival in Pyin Oo Lwin, Myanmar, 25 November 2015. During the festival, hot air balloons made of multicolored papers and hung with paper lanterns, fireworks and fire sticks are exploded in mid-air. (Photo by Hein Htet/EPA)