LOS ANGELES:  Animals can melt the human heart, tickle the funny bone or bring us to tears. And thanks to Instagram, YouTube and other online options, you can enjoy their antics simply by following, liking or pinning them.

Dr. Bonnie Beaver, executive director of the American College of Veterinary Behaviorists and a professor at Texas A&M University's College of Veterinary Medicine, says two things make animal photos and videos so popular.

— Many animals have physical traits that subconsciously cause humans to nurture, like large, round heads and large eyes. Think E.T.

— Many images show animals doing something unexpectedly clever, human-like or just plain cute — kittens trying to run up a slide, for example, she said.

The Associated Press got hooked on six animals in 2015, from dogs and cats to a panda and a rat, whose popularity is likely to continue into the new year. Here's a look.