Even from a distance, dogs key into each other's body language — friendly or not. Their postures and behaviors can also help owners determine if an introduction is appropriate.

Interpreting a dog's body language can be tricky, according to behavior experts. With that in mind, it's generally better to take a conservative approach and skip the greeting if either dog appears fearful or feisty, says Jean Donaldson, director of the Academy for Dog Trainers at the San Francisco Society for the Prevention of Cruelty to Animals.

"Lunging, snarling, snapping, and growling don't guarantee that a dog is dangerous, but it's not wise to risk a scuffle," Donaldson suggests. A dog that seems uncomfortable around another dog shouldn't be forced into an introduction, she adds. Cowering, shrinking himself, attempting to flee, or retreating behind his owner's legs can all indicate a dog's fear.

When you do permit your dog to say hello, keep watch and interrupt gently, if necessary. Simply walk away, using a pleasant command. Don't yank your dog's leash abruptly or use harsh tones, or you may fuel an already tense encounter.

An interruption might be warranted if the dogs hold stiff postures for more than a few seconds, according to Donaldson. If one dog puts his chin or paws over the neck of the other dog, walk off before tension heats up, she says.

Although body language can be ambiguous, some behaviors are fairly reliable indicators of happy encounters. "If a dog is wagging and wiggling at the other dog, we love that,'' Donaldson says. "If both dogs are not wagging and wiggling, keep it brief."

Dog behavior is useful, but focusing on a single aspect or body part can be misleading, according to Pamela Reid, vice president of the ASPCA Animal Behavior Center. "It's like taking a quote out of context,'' she says.

In addition to body language, decisions about introductions also should be based on your dog's previous social experiences. If dogs tend to be scrappy with peers, refrain from greetings and seek a professional trainer or behaviorist to work on that issue.