Knight Ridder News Service

There are now more cats than dogs in the United States (78 million cats vs. 65 million cats in 2003, according to American Animal Hospital Association and the American Pet Products Manufacturers Association). So, here are feline facts to amaze, delight and inspire anyone from the ailurophile to the casual cat fancier:

• Kittens are born blue-eyed. If their eyes change colors, it generally occurs at 4 to 5 weeks of age. Kittens open their eyes at 7 to 10 days but can't hear until they're about 14 days old.

• The cat is the only animal that purrs. Domestic cats "sing both ways" and can purr while inhaling or exhaling, while the big cats (lions and tigers) can only purr while exhaling.

• Cats lick themselves "clean" right after dinner because instinct has taught them the sooner they remove food odors, the less likely cat predators will get a whiff of McCat. Cats bury their waste to hide evidence from predators and avoid territorial turf battles with other cats.

• When a domestic cat goes mousing, it gets fast food about every third pounce. Of course, most house cats have evolved from mouser to moocher.

• Among the world's greatest cat haters were Genghis Khan, Alexander the Great Julius Caesar, Napoleon and Hitler.

• Kitty Litter was invented in 1947 when delivery man Edward Lowe, who was out of sand, suggested to a cat owner that she use a grease and oil absorbent (a clay called sodium bentonite) instead.

• The collective term for a group of adult cats is called a clowder.

• The term "cat's pajamas" comes from an English tailor of the late 1700s and early 1800s who made the finest silk pajamas for royalty and other rich patrons. His name was E.B. Katz.

• A cat can turn its outer ear toward a sound about 10 times faster than a dog. Furthermore, a cat, with more than 40,000 nerve fibers in its ears, can hear sounds (like the can opener) up to two octaves higher than humans.

• At the back of a cat's foot is a single carpal pad that doesn't touch the ground. It is thought to act as a brake when the cat leaps forward or stops from speeds that can reach up to 31 mph.

• Cats are the only species that can hold its tail vertically while walking, according to Cat Fancy magazine.

• Cats purr at the same frequency of 25 vibrations per second, their temperature is about 102 degrees Fahrenheit and their heart beats about 155 times per minute.

• Cats' eyes appear to glow at night because of a layer on the back of the retina called the tapetum lucidium, which possesses crystal-like reflective properties. Cats can see in low light but not in total darkness.

• About 50 percent of cats have the gene that allows for catnip crazies and get a hallucinatory high from eating, smelling or rubbing catnip.

• The U.S. superstition about having bad luck if a black cat crosses your path grew from the belief that the cat was on its way to visit the devil. In Britain, black cats are considered good luck.

• A cat generally has 24 whiskers (called vibrissae), 12 on each side of its face. The whiskers are divided into upper and lower rows, which move independently of each other and are used to help cats detect objects in low light and aid their ability to slip through narrow openings.

• Talk about a cat nap: Seventy percent of each cat's day is spent dozing. Thirty percent of its awake time is spent grooming.

• When cats arch their backs towards human hands, like a hearty, hairy handshake, they're exhibiting mutual endearment. When cats collapse on their backs with their paws in the air, beware. They're telling you to give them space.

Dr. Marty Becker is veterinary contributor for ABC's "Good Morning America."