A competitor participates in the Tough Mudder challenge near Henley-on-Thames in southern England May 2, 2015. (Photo by Eddie Keogh/Reuters)

A helicopter drops water over a wildfire as a firefighter works to contain it in Benahavis, southern Spain, May 19, 2015. (Photo by Jon Nazca/Reuters)

A participant smiles at the annual Christopher Street Day parade on Kurfuerstendamm in Berlin, Germany, June 27, 2015. (Photo by Fabrizio Bensch/Reuters)

Four-month-old fox cubs squaring up to each other in Walthamstow, England on August 7, 2015. (Photo by Greg Morgan/Barcroft Media)

Attendees at Wizard World Comic Con walk through hallways in Chicago, Illinois, United States, August 22, 2015. (Photo by Jim Young/Reuters)

Andy Goldfarb, a staff biologist at the Point Defiance Zoo & Aquarium, plays with one of the four clouded leopard cubs currently at the zoo Friday, June 5, 2015 in Tacoma, Wash. The quadruplets were born on May 12, 2015 and now weigh about 1.7 lbs. each. Friday was their first official day on display for public viewing, usually during their every-four-hours bottle-feeding sessions, which were started after the cubs' mother did not show enough interest in continuing to nurse them. (AP Photo/Ted S. Warren)

Ford is celebrating the 50th anniversary of the Mustang with a limited-edition model and a display atop the Empire State Building. The car had to be broken into five pieces for the ride up the building’s elevators and reassembled late at night, when the deck is closed to visitors. Photo: The 2015 Ford Mustang convertible, assembled overnight, sits on the observation deck of the Empire State Building. (Photo by Hiroko Masuike/The New York Times)

Pilgrims wearing traditional dresses take part during the Queen of Angeles pilgrimage in Alajar, southern Spain, September 8, 2015. Every year, devotees converge at the Arias Montano crag to pay homage to the Queen of Angeles during an annual pilgrimage which combines religious fervour and festive colour. (Photo by Marcelo del Pozo/Reuters)