Barn cats, alley cats, Siamese cats, Persian cats-to many dog lovers, cats are not tolerated and are simply considered the "other" pet. After all, we are "dog people"-cats are nice, but dogs are our passion.

Cats, though, are tiptoeing into countless homes, blurring the line between dog and cat lovers. People are discovering that the two species can co-exist peacefully, meaning that breeders and dog trainers increasingly are being asked to help the process along and to explain differences between the two.

Kittens and adult dogs must be supervised when first introduced, so that neither animal gets hurt. But it is not unusual for the animals to become fast friends despite their biological differences.

To some dog lovers, cats are mysterious, alien beings. They may even arrive in strange ways, appearing one day and behaving as if they've always lived on the premises. Sometimes a dog is the first to notice the newcomer. Lacey, a Pomeranian, was making a property check on a frigid, winter day when she discovered a very young kitten lying in a drainage ditch. She immediately raced back to the house and made it clear that a rescue was necessary, and owner Maria Betlinski took the feline in.

The kitten, whom Betlinksi named Independence, began to live among more dogs than most cats see in a lifetime. The household dogs noticed that the kitten seemed to have no desire to bicker over rank and privileges, which suited them.

Betlinski was amazed at how quickly Independence imitated many of the dogs' social behaviors directed toward her. While this was going on, she began to shape the kitten's household manners using positive reinforcement for behaviors she liked. Despite beliefs to the contrary, cats, she discovered, could be trained like dogs-with some important distinctions.

Cathy Crawmer, a professional animal trainer and author of Here Kitty, Kitty agrees. Those in the dog world may best know Crawmer from video footage shown at clicker-training seminars where she is shown training a cat to run an agility course.

Crawmer emphasizes one learning characteristic that differs between dogs and cats: a cat's attention span is very short. "The average cat will work for 5 to 10 rewards, and that's it!" Crawmer says, while a dog will hold its concentration on the trainer a lot longer.

Cats are easily distracted. In the midst of highly reinforcing activities a cat may turn his attention abruptly to something else. By comparison, most dogs can be motivated to remain on human-directed tasks for a much longer. This may be the reason that most people assume cats can't be obedience trained.

Fighting, Well, Like Cats and Dogs
Dogs, as well as humans, must learn the unique aspects of cats if they're to live together. But in many ways, dogs have a much more difficult time than we do.

"Dogs speak Doggish, cats speak Cattish, and very frequently the same signs can mean exactly the opposite," says Stanley Coren, Ph.D., psychology professor at University of British Columbia and author of How to Speak Dog (Free Press). He believes that quite a bit of the distrust and animosity that exists between dogs and cats stems directly from misinterpretation of body language.

He points to tail wagging as an example. In cats, tail-swinging is a "keep your distance" signal, while in dogs a relaxed wag is a friendly sign. Dogs raise and stiffen their tails to signal dominance, whereas cats raise theirs to indicate friendliness. A cat's upright tail combined with piloerection indicates fear, whereas a stiff, upright tail in a dog whose hackles are raised indicates assertive, aggressive intent. It's easy to see how the misreading of tail signals alone can result in trouble for both species.

Rolling on the back is another feline behavior that dogs might misinterpret. Dogs consider this a sign of submission. Cats use the behavior to expose teeth and all claws in order to grasp, bite, and disembowel prey. When a cat presents this behavior, he's ready to attack. But to the dog, the behavior appears friendly, so he might decide to sniff out his roommate and receive an unwelcome surprise.

Coren says that dogs can learn to read cat signals just as they learn to read human ones-by trial and error. He says that a puppy and kitten raised together appear to work out communication problems with the least amount of difficulty, probably due to their size and strength. Adult dogs and cats must be supervised when introduced, with human intervention if needed, so that neither species sustains physical damage as they learn. If a peaceful co-existence seems improbable, common sense dictates that one or the other species isn't up to the task.

In Betlinkski's home, the resident dogs accepted the kitten, and eventually two more cats moved in. Cats, if you recall, have a way of doing that. And although as a dog lover you may swear that only canines will cross your threshold, it may be one of your own dogs that changes your mind. Just ask Maria Betlinski.

Margaret Gibbs has a master's degree in clinical psychology and is a professional dog trainer, behavior counselor, and author.