Q: Is it really true that when a dog’s nose is cold and wet, it means she’s healthy?

A: Sort of. To really get to the bottom of this, we need to understand why a dog’s nose is wet in the first place.

Tears are constantly produced to lubricate the movement of the eyes. Because this lubrication is so critical to eye health, the dog’s body routine produces more tears than are needed. These excess tears flow through the naso-lacrimal (literally “nose-tears”) duct and out the base of the nose. (People experience this when crying.)

As the tears drip down into the dog’s face, the dog licks her nose, spreading the tear fluid over the nose, which wets it. Then, evaporation causes the nose to be cool. The moistened nose is better equipped to dissolve airborne chemicals, which contributes to a better sense of smell.

When a dog is sick, the body uses up more internal water in the process of fighting disease. This increased use, especially with a fever, causes relative dehydration, even if the dog is drinking a normal amount of water. This dehydration results in deceased tear production, and hence a dry nose.

However, the same dry nose could be because of fluid loss from panting on a hot day. Some dogs (such as poodles and Lhasa Apsos) often get reddened cheeks from blocked tear ducts, so there is less fluid flowing through the ducts to moisten the nose.

The bottom line is that the dry nose is one indicator of hydration, but it indicates illness only if it’s coupled with lethargy and other symptoms.

Q: Does a wagging tail always mean a friendly dog?To get a read on a dog’s attitude, it’s important to look at the whole dog. A dog who’s up on her toes with her eyes focused in a hard stare and hackles raised may well have her tail up and wagging — but she is not a friendly dog.

A:

A dog who’s relaxed, smiling in a doggy grin and wagging her tail in a lower position is more likely to be friendly.

A nervous dog who may snap from fright may also be wagging her tail, but it’s likely to be held lower.

Q: What is it about the way cats walk that always makes them look so elegant and smooth? If you’ve ever carefully watched dogs walk, you may have noticed that they alternate sides when they step. The front right paw steps forward at the same time the rear left paw does. Then the front left and rear right paws step out. Speed this up and it’s known as a trot.

A:

Cats move differently. They step with both left paws, then both right paws. Their natural gait, in other words, is what’s known as a pace. (Only camels and giraffes have the same natural gait, although some horses are trained to race using the pace.)

One thing cats and dogs do have in common: They walk on their fingers and toes.

Most cats have five toes on their front paws, but only four of them hit the ground. The fifth toe is called a dewclaw, and is found on the inside of the front paw. The dewclaw is the feline equivalent of our thumb, and it’s used for grasping prey and climbing trees. A normal feline back paw, by the way, has four toes that are all called into service when walking.

Q: Why do cats’ eyes shine at night? Cats’ eyes are more sensitive to light than ours are, which means they can see a lot better in low light than we can — which is what you’d expect from a nocturnal animal. Even cats can’t see in total darkness, but they can get pretty close.

A:

One of the most visible (pardon the pun) ways they’ve adapted to low-light conditions is revealed in those glow-in-the-dark eyes.

The glow is actually light reflected back from a layer of special cells behind the retina, called the tapetum lucidum, which is Latin for “luminescent tapestry.” The retina is the light-sensitive tissue lining the back of the eye. Its job is to convert light into electrical impulses that are sent to the brain. The tapetum lucidum catches all the light that didn’t enter the retina directly and reflect it back in, so every bit of light can be processed.

Add in the fact that a cat’s pupils can dilate to three times the size of ours and they also have a larger cornea, and you can see why a cat has no need for night-vision goggles. The bottom line: A cat can see in conditions that are more than five times less bright than what we require.

Ancient Egyptians had another theory for why the cat’s eyes glow at night: They believed the eyes of a cat reflected the sun, even at night when it was hidden from humans.

Dr. Marty Becker is the resident veterinarian on “Good Morning America.” Gina Spadafori is a syndicated pet columnist. Their two new books are “Why do Dogs Drink out of the Toilet?” and “Do Cats Always Land on Their Feet?”. Look for more dog and cat answers from these books in The (402).