Animals like to play for many of the same reasons human children and adults like to play. Physical play helps to reduce stress levels, and most animals in the wild are constantly under stress, either to hunt for food or avoid being hunted. Any opportunity to spend a few worry-free minutes engaged in mindless play is an opportunity worth taking in the animal world. Spending an entire day in a state of tense watchfulness, which many prey animals do, can be very damaging to an animal's nervous system and mental acuity. Play also helps animals form stronger bonds with their pack or owners.
Another reason animals like to play is to keep their natural survival skills sharp. What owners may consider playful activity is actually an instinctive behavior to a pet, such as climbing trees, pouncing on toys and running after humans. A dog with a strong herding instinct, for example, will engage in a type of play that involves "herding" their "family members." A cat will pounce on a small toy because that is the same action he or she would use to trap a real prey animal in the wild.
Guinea pigs, hamsters, gerbils and other prey animals like to play games which mimic their natural escape and hiding instincts. A prey animal kept as a pet will often scurry into a tube or a habitat home as a way to keep his or her escape instincts sharp. Climbing over objects and finding new places to hide are also part of both prey and predator animals' play, since a predator animal uses stealth to hunt and a prey animal uses camouflage to hide.
Cat toys and dog toys are often designed to mimic their natural food sources or prey. Predator animals like to play with toys that react like the real thing, such as a squeaky mouse-shaped toy that duplicates the sound of an injured or dying animal. The texture or shape of a dog or cat toy could also be very appealing to a pet who still has the natural instincts of its breed to chew, scratch or trap. Playing with these toys helps a pet to satiate these natural urges without causing significant damage to real humans or other pets.
Some animals like to play because it keeps them in good physical condition. A prey animal may have to run great distances at top speed in order to avoid a predator. A predator animal may have to chase his or her prey at top speed until it is captured. By using an exercise wheel or running in the backyard, a pet can maintain good cardiovascular health and improve its stamina. Physical play with human owners and other animals helps to establish stronger social bonds, which many pack animals crave naturally.