No matter how you play with your dog, you might have the type of dog who tends to get overly aroused when she gets excited. Just like some children, some dogs come hard-wired to spiral into a state of emotional overload in seemingly low-key situations. Other dogs, especially adolescents, haven’t yet perfected their emotional thermostats, and need their owners to help them learn to keep their emotions in check. In either case, all dogs need their owners to know the signs of over arousal, and to know how and when to calm things down before they begin to spiral out of control.

Begin by carefully observing your dog during regular play. Watch the way her body moves, and the way he eyes look. Listen carefully to her barks and play growls, if she’s the kind of dog who vocalizes while playing. Become familiar with her normal repertoire, because dogs tend to do the same kinds of things when they get overly aroused, just more so. In general, their movements are faster, their leaps are higher, and their barks are louder. Sometimes you’ll notice that their movements look less coordinated and less precise, as though they are physically spinning out of control (which they are!). If a dog has been play-growling, listen for the growls to get lower and to sound more threatening. On the other hand, listen for barks to become more rapid and, ironically, higher-pitched.

Some dogs add actions to their regular bag of tricks when they become overly aroused. Dogs who were politely playing tug or fetch might start leaping up and nipping at your arm. Be especially careful if your dog starts leaping up at you repeatedly, perhaps pushing off you with her forepaws, punching you with her muzzle, or clacking her teeth together while her head is directed toward you. These are dogs who might be losing emotional control or are becoming over aroused, and are telling you that you’re going to be the target of their pent-up, uninhibited, energy. If this happens, it’s time to put your inner playground monitor on duty. We’ll explain how to do that in the next section!

Other signs that a dog is overly aroused include a retraction in the corners of the mouth as though the dog is panting from extreme overheating (but it’s not that hot). Another good predictor of over arousal is a dog who simply can’t stop doing what she’s doing—you call; ask her to sit, come, or lie down; and she continues leaping or barking in an out-of-control kind of way. Fixed and rounded eyes can also be a sign that a dog is emotionally overloaded, and are another good reason to develop a precise picture of how your dog looks when playing appropriately.

There is another important behavior to watch for that is not necessarily related to arousal, but is potentially dangerous. If your dog has a closed mouth, along with a stiff and still body, she may be sending you a warning that a bite is on the way. Dogs who are playing politely will often stop for a second or two and look at you (a kind of self-imposed doggy time-out that prevents over arousal) but their bodies stay loose and relaxed and their mouths are usually open. However, if your dog stops all play, goes stiff and silent, and her eyes become hard and round while she stares directly at you, immediately try to break the mood by saying “Want your dinner?” or “Let’s go for a walk!” and walk away. Your next step is to pick up the phone and call a good trainer or behaviorist.

If you are unsure if your dog’s behavior is within the bounds of normal play, don’t hesitate to work with an experienced trainer or behaviorist. It’s not uncommon when you are first learning to read visual signals to start worrying about postures and expressions you never noticed before. It happens in many fields—young biology students discover that the world is awash in bacteria and begin to obsess about what’s on the doorknob. Medical students memorize the symptoms of obscure diseases and begin to imagine they have come down with them. So, if a little knowledge begins to feel like a dangerous thing, go out of your way to work with someone more experienced who can help you decipher your observations.

(This is an excerpt from the new book, "Play Together, Stay Together: Happy and Healthy Play Between People and Dogs" by Karen B. London, Ph.D. and Patricia B. McConnell, Ph.D.)