Every dog owner has experienced it at one time or another. Your dog lies down, often with his head on his front paws, and lets out a sigh. Is he sad? Content? Disappointed in his life?

It could be any of the above, it just depends on the context, says the American Kennel Club.

"When the sigh is combined with half-closed eyes, it communicates pleasure; with fully open eyes, it communicates disappointment: 'I guess you are not going to play with me.'"

Geez. Guilt trip, anyone?

A dog's sigh is "a simple emotional signal that terminates an action," writes Stanley Coren, Ph.D. in his book, "Understanding Your Dog for Dummies."

"If the action has been rewarding, it signals contentment. Otherwise, it signals an end of effort."

So if you and your dog just finished a fun romp in the yard or a great walk in the park, that sigh means, "I'm content and am going to settle down here awhile." If your dog has begged at your side all during dinner without a payoff, that sigh signifies, "I'll give up now and simply be depressed."

Dog trainer Pat Engel agrees.

"My own unscientific observation is that dogs usually sigh while resting, or when they are what I call 'resigned,'" she writes in the San Francisco Chronicle. "These sighs seem to mark a physiological transition into a deeper state of relaxation."

If you feel like your dog sighs (or yawns or makes other noises excessively), it's worth mentioning to your vet, Engel suggests. There's always a chance that a health issue might be at the root of the sounds.

If a medical reason isn't to blame, then concentrate on reading the cues your canine is sharing.

Massachusetts dog trainer Jody Epstein says a dog's body language is definitely the key to interpreting the noise he's making.

"If his body is relaxed, ears soft, head down on the bed in what we might call a 'sleeping' position, and he's in perfect health otherwise, then I'd expect it's just a sign of uber relaxation," she writes in her All Experts advice column. "If he's laying there, but sitting up watching you and doing it, then it's more likely an active communication that you may wish to address."

Like, hey, buddy, isn't it time for a treat? Or when was the last time we played ball?

dog looking sad or sighingOne dog may sigh because he's frustrated; another may sigh because she's comfortable and is ready for a nap. (Photo: Brent Schumacher/flickr)

Is a sigh always a sigh?

"Dogs make many vocalizations, and they mean different things depending on various factors such as context, experience, relationships, the individual dog, and much more," says certified animal behaviorist and dog trainer Katenna Jones of Jones Animal Behavior, in Warwick, Rhode Island. "There is also human interpretation: One person's sigh is another person's huff, moan, groan or whine."

And, Jones says, some breeds tend to make more or different sounds than others.

"The most important thing is to remember there is no one answer. It's important to not apply human feelings to dogs because dogs are not humans!" she says. "Look at the context of situations in which your dog is sighing, take note, and see if you can identify why YOUR dog is sighing — because it may be different than why MY dog is sighing."

Just because we don't always know what our dogs are trying to say, doesn't mean we should stop trying to figure things out.

The AKC points out: "Dogs make sounds both intentionally and unintentionally, and they all have certain meanings. Just because we do not understand the wonderful variety of sounds that dogs vocalize does not mean that dogs are not doing their best to communicate with us."

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.