Cats are subtle.

This, of course, is the whole point, say their fawning humans. Disdainful of the panting, pawing, woofing neediness of that other species with which they often share domiciles, cats generally are the proverbial still streams.

But when they are sick, these consummate stoics also can lead lives of quiet desperation that go unnoticed by all but the most attentive human.

“Cats are like snowflakes — they’re all similar, but different,” says veterinarian James R. Richards, director of the Cornell Feline Health Center at Cornell University College of Veterinary Medicine in Ithaca, N.Y. The one thing they do share is an all-too-deft ability to hide illness and pain. “If people would become cat watchers — an act that I find joyful, because they’re such a hoot to observe — we might discover really significant illness that may not have manifested yet.”

The key, says Richards, is learning to recognize what is normal behavior for your particular cat, so that deviations from it become readily apparent. In addition, schedule twice-a-year wellness checks, instead of annual ones.

Being the reserved, majestic creatures that they are, cats have a relatively limited repertoire of ways to communicate that there is something wrong, Richards says. Among the signs:

Changes in behavior. Cats are creatures of habit, so watch for a break in routine, however subtle — such as not greeting you when you arrive home, or hiding more than usual under furniture.

Another warning sign might be a cat that routinely sleeps on top of the counter but now has abandoned that post for a different one, or is sleeping for more hours, or during different hours.

“They’re not the kind of jab-you-in-the-rib changes that sometimes we’ll see with dogs,” Richard says, but they might be cause for concern.

Increased activity isn’t always a good thing, either.

“If your cat’s acting like he’s had five cups of Starbucks, don’t just dismiss it as ‘My old cat’s feeling frisky,’ ” he warns.

It could be something more serious, such as hyperthyroidism.

Inappropriate elimination. Litter box woes are a common theme among cat owners. Often they are caused by emotional turbulence in a cat’s environment — the arrival of a new animal, a change in human residents.

A change to the litter box itself also can disrupt potty patterns: A new lid on the box or a switch in brands of litter is sometimes all it takes for a kitty to go AWOL.

But a physical problem may be the culprit. If urinating causes pain, a cat may associate it with the box and so might avoid it. Some intestinal problems or diabetes can cause increased eliminations and more “misses.”

“Sometimes you have to be a detective to figure out what’s going on,” says Richards, who suggests scrutinizing the litter box to see if there is any change in the volume or consistency of stool, or the wetness of the litter itself.

Changes in appetite. In multi-cat households where cats are free-fed, monitoring eating patterns can be a challenge. Loss of appetite is an obvious red flag, but overeating can point to a physical problem, too.

Changes in odor. In cats, bad breath is more than just a turn-off; it can be a sign of periodontal disease. Oral cancers also can go unnoticed.

Changes in grooming. If you’re feeling under the weather, the last thing you want to do is get all dolled up. So look more closely at that cat with an unkempt coat. Watch for bare spots or a difference in fur texture.

“Grooming behavior takes up a good part of a cat’s day,” Richard says. “Cats may stop if they don’t feel well, or if it’s painful to groom — if they have severe arthritis, maybe it’s hard to get their tongue to certain parts of their body.”

Changes in vocalization. As much as you may relish the silence, pay attention to the talkative cat who now is quiet as a church mouse.