A tourist poses for a picture with the Sphinx at the Pyramids of Giza in Cairo, Egypt, on October 19, 2011. (Reuters/Jamal Saidi)

Participants wearing masks during a hazy day at the Beijing International Marathon in front of Tiananmen Square, in Beijing, October 19, 2014. (Photo by Reuters/Stringer)

Injured horses huddle together in Oklahoma City on Monday. (Photo by Chris Landsberger/The Oklahoman)

Students pose for a pictures taken by their friends during spring break on the beach in the resort city of Cancun, Mexico, February 27, 2009. (Photo by Israel Leal/AP Photo)

Denver Broncos cheerleaders during the third quarter. The Denver Broncos played the Kansas City Chiefs at Sports Authority Field at Mile High in Denver, Colo. on September 14, 2014. (Photo by Aaron Ontiveroz/The Denver Post via Getty Images)

White lioness Azira lies in the cage with her three white cubs, on February 4, 2014. Zoo owner Andrzej Pabich says white lions often have defects that prevent giving birth, or the mother rejects her cubs, but Azira has been patiently feeding and caring for her little ones. (Photo by Czarek Sokolowski/Associated Press)

A young oriental small-clawed otter at the zoo in Neumuenster, Germany, March 5, 2014. The six young otters (one male, five female) were born on December 7, 2013. (Photo by Maja Hitij/EPA)