"Animals also experience immense joy when they play, greet friends, groom one another, and are freed from confinement. They even seem to enjoy just watching others having fun. Joy is contagious.

"Animals tell us they are happy by their behavior — they are relaxed, walk loosely as if their arms and legs are attached to their bodies by rubber bands, smile, and go with the flow. They also speak in their own tongues — purring, barking, or squealing in contentment. Dolphins chuckle when they are happy. African wild dogs greet one another with squealing, propeller-like tail wagging, and bounding gaits. When coyotes or wolves reunite, they gallop toward one another whining and smiling, their tails wagging wildly. They are jubilant upon meeting, licking one another's muzzles, rolling over, and flailing their legs. When elephants come together after being apart, there is a raucous celebration as they flap their ears, spin about, and emit a 'greeting rumble.' They are so happy to see one another.

"Joy abounds in play. Animals become deeply immersed in the activity and show their delight by their acrobatic movements, gleeful vocalizations, and smiles. There's a feeling of incredible freedom in the flow of play. Violet-green swallows soar, chase one another, and wrestle in grass. I once saw a young elk in Rocky Mountain National Park run across a snowfield, jump in the air and twist his body while in flight, stop, catch his breath, and do it again and again. Buffaloes have been seen playfully running onto and sliding across ice, excitedly bellowing gwaaa! as they do so.

"As I point out in my book The Emotional Lives of Animals (2007), numerous studies demonstrate that there are neurochemical bases for why play is enjoyable, and that the same chemical changes occur in both animals and humans during play. A boy and his dog wrestling in the yard are not only both playing — they both are getting the same pleasurable feelings from doing so. Neurotransmitters such as dopamine and perhaps serotonin and norepinephrine are important in the relation of play, and large regions of the brain are active during play. Rats show an increase in dopamine activity simply anticipating the opportunity to play. Opioids are also linked to play. These neurochemicals are related to feeling relaxed or 'socially comfortable,' a condition important for facilitating play.

"The more we study animal emotions and the more open we are to their existence, the more we learn about their fascinating emotional lives. Surely, it would be narrow-minded to think that humans are the only animals who have evolved and experience deep emotional feelings."