All pets love to play. From the littlest puppy and kitten to even a fairly elderly cat or dog, play should be an important part of the pet's daily routine. It's not just a chance to exercise -- which is something both pets and their human caretakers can always use. Play also helps condition pets to acceptable and appropriate behavior. But not all play is good. In fact, certain types of play may inadvertently teach pets to be aggressive or otherwise encourage bad habits.

One example is tug of war. Veterinarians and animal behaviorists especially caution against playing tug of war with young puppies. Puppies greatly enjoy this game -- so much that even after you've stopped, they will continue to play with anything that provides resistance -- like your curtains, the sofa or the carpet.

Tug of war can bring out aggressive behavior in the dog -- snarling, growling, biting the item, pulling and shaking the person on the other end. These are not traits that most pet owners -- particularly those with small children -- want to encourage in their dog. Instead, try a nice game of fetch.

(Thanks to Mariam Yarden, an animal behavior specialist in Long Beach, California for suggesting this topic and for her input.)