In this Wednesday, August 2, 2017 photo, Borre, an 8-year-old cat sits in a basket next to the canal on the Catboat shelter in Amsterdam, Netherlands. In the heart of the Dutch capital, on a canal near one of the busiest shopping streets, a floating animal sanctuary called The Catboat provides refuge for about 50 stray and abandoned felines. (Photo by Muhammed Muheisen/AP Photo)

Dancers at the Windmill Theatre in London, England practice a routine wearing gas masks and hard-hats with their costumes, 1940. (Photo by Hulton Archive/Getty Images)

Andrey Karr from Western Riders Slacklines at sunset above big waves in Nazare, Portugal on December 27, 2017. (Photo by Aidan Williams/National Geographic Travel Photographer of the Year Contest)

Lindsay Heimbach goes airborne while sledding down a hill on Mt. Lemmon December 27, 2008. (Photo by James Gregg/Arizona Daily Star)

A passenger plane comes into land over a field containing horses at Heathrow Airport on August 11, 2014 in London, England. Heathrow is the busiest airport in the United Kingdom and the third busiest in the world. The airport's operator BAA wants to build a third runway to cope with increased demand. (Photo by Peter Macdiarmid/Getty Images)

Framed by the setting sun, an American Bison grazes at the Tallgrass Prairie National Preserve on Tuesday, April 28, 2015, near Strong City, Kan. The buffalo herd at Tallgrass is one of the few herds of wild bison left in the United States. (Photo by Travis Heying/The Wichita Eagle via AP Photo)

Participants of the techno-parade “Zug der Liebe” (Train of love) dance on a street in Berlin, Germany July 25, 2015. The “Zug der Liebe” is the successor to the “Loveparade”, which in its heyday attracted up to 100,000 participants and ended in disaster and tragedy in 2010 when 21 people died and over 500 were injured due to suffocation from overcrowding at the “Loveparade” in Duisburg. (Photo by Axel Schmidt/Reuters)