Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)

A red fox sits in front of a Eurofighter Typhoon combat jet on the grounds of the 2014 ILA Berlin Air Show, in Selchow near Schoenefeld, Germany, Thursday, May 15, 2014. The International Aviation and Aerospace Exhibition ILA will take place from May 20 until May 25, 2014. (Photo by Patrick Pleul/AP Photo/DPA)

A dejected German Grenadier carrying a machine gun on his shoulder in front of a building on fire during the German retreat in Russia. (Photo by Keystone/Getty Images). 1944

Catherine, Duchess of Cambridge speaks to soldiers as she arrives at Calgary Airport on July 7, 2011 in Calgary, Canada. (Photo by Chris Jackson/Getty Images)

A girl looks with comic disgust at a guy who falls asleep with a bottle of beer at a party; her friend laughs. (Photo by Edward Corbett/Rex Features/Shutterstock)

Pоrn actresses take a break at the Venus erotic fair in Berlin, Germany, October 15, 2015. The event, which represents the erotic business in the German capital, is open till October 18, 2015. (Photo by Fabrizio Bensch/Reuters)

After 12 years photographing models, musicians, and celebrities, Brad Wilson decided that he wanted to photograph something a little more unpredictable: wild animals. Photo: Serval. (Photo by Brad Wilson)

In this November 28, 1966 file photo, one of the 10 beagles involved in the first test of the Veterans Administration Hospital in East Orange, N.J. smokes a cigarette through a machine linked to its windpipe by a plastic tube to test any link between smoking and emphysema. (Photo by AP Photo)