You’ve all heard the gag. It’s the one about the guy who goes to the doctor with an unidentified malady then has a cat walk around him and a Labrador retriever sniff him before the doc hands him a big bill for a “cat scan” and “Lab test.” (I know. It was funnier the first time.) But as all jokes go, there’s a bit of truth behind the humor.

As most of us pet watchers already know, pets are excellent sentinels for disease.

One recent example in the medical literature demonstrated that dogs trained to detect the aroma of lymphoma cancer cells in urine did so quite accurately. One dog went so far as to inform the researchers that their control group (unaffected by cancer) was currently suffering from a previously undetected kidney malignancy.

Another great example of uncanny accuracy in disease process recognition involves the success of dogs in predicting seizures. Many people with epilepsy now rely on trained dogs to signal when they’re about to have a seizure so they can get in a safe place and position.

These examples tell us nothing many of us weren’t convinced of just by paying attention to our pets’ behavior. When we’re sick they act funny. I know a woman who swears by her tried and true method of ascertaining whether her preschooler is going to wake up with a fever. The cat sleeps at the child’s door all night. I’m sure a lot of you have similar stories.

If dogs are sensitive to the impending signs of organic disease manifestation in humans it stands to reason they might be more so when it comes to their own. One well-documented scenario involves inter-cat or inter-dog aggression. In these cases, dogs that have always gotten along perfectly well will suddenly start fighting or avoiding one another. Cats do it, too.

A few years ago my own dogs started fighting weeks before one started having seizures. He was later diagnosed with a brain tumor. Ever since, I pay close attention to dogs and cats with bite wounds sustained from their household brethren. I often ask to see the aggressor as well, offering full work-ups of all pets involved should the aggression persist and no obvious behavioral cause present itself (a move, new baby, etc.).

Over this last weekend my mother’s dogs were suddenly at odds. Her hellion of a Jack Russell turned into a submissive shrinking violet when faced with her normally mild, dingo-dog housemate. We were mystified when they fought over Sunday’s breakfast. (Wow! They’ve never done that before.) By Sunday night the Jack’s neck was bleeding from a [previously undetected] abscessed puncture wound she’d obviously sustained days before (probably tussling with an opossum in her wooded yard).

Sometimes the “cat scan” and “Lab test” are far more sensitive than anything science can devise. It’s worth our while to keep this in mind. If only I’d done so I might have spared my mom’s Jack a few hours of pain and stress. She perked right up after a Sunday night trip to the vet for fluids and antibiotics. Lucky for her she’s got an aunt in the business.

Here's a pic of the dingo-dog (Miss Brown) and another of the usually terror-inspiring Jack (Flor) pictured with my son during her hospital visit.