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

A woman takes part in an extreme run competition in Zhodino, east of Minsk, September 26, 2015. (Photo by Vasily Fedosenko/Reuters)

People are reflected in mirrors as they walk in a busy shopping district in Tokyo, Japan, December 25, 2015. (Photo by Thomas Peter/Reuters)

Newborn sea lion “Kaya” crawls at the enclosure at the zoo in Wuppertal, Germany July 23, 2015. Kaya was born on July 4, 2015 in the zoo, officials said. (Photo by Ina Fassbender/Reuters)

The Swiss Federal Palace (Bundeshaus) is illuminated by giant light projection "The Jewel of the Mountains" in Bern, Switzerland October 15, 2015. The light and sound show will run every evening until November 29, 2015. (Photo by Ruben Sprich/Reuters)