A mother and calf humpback whale swim in the Exmouth Gulf in Western Australia. Fredrik Christiansen/Functional Ecology hide caption

Say what you will about naked mole-rats, but their bodies have a trick that lets them survive periods of oxygen deprivation. Roland Gockel/Max Delbruck Center for Molecular Medicine hide caption

An Army horse wears a gas mask to guard against German gas attacks. Courtesy of U.S. National Archives hide caption

In a photograph taken Saturday, volunteers prop up a pilot whale at Farewell Spit in New Zealand. Overnight, more than 200 of the stranded whales returned to the sea. Marty Melville/AFP/Getty Images hide caption

A group of false killer whales is stranded near the Florida Everglades. AP hide caption

Flowers and sympathy cards for Harambe the gorilla at the Cincinatti Zoo. This year was one for celebrity deaths, human and animal alike. John Minchillo/AP hide caption

Researchers found that rats experiencing positive emotions had an increased pinkish hue on their ears, like the animal on the left. The animal on the right is from the control group. Plos One hide caption

Mental illness can be isolating, making the companionship of pets even more precious. Gary John Norman/Getty Images hide caption

A giraffe in Kenya. Khaled Kazziha/AP hide caption

Trail cameras in Gardner, Kan., captured wild scenes from a local park — just not the type of scenes police were expecting to see. Gardner Police Department hide caption

In Zimbabwe's Hwange National Park, elephants drink from a watering hole. Winfred Wisniewski/Getty Images hide caption