18 Surprising facts about our feline friends.

Cats are known for their poker faces. They don't always reveal what they're thinking or feeling, a trait that may contribute to their reputation as animals of mystery and intrigue. So here 18 surprising facts about cats that even the most dedicated cat lovers might not know.

• Cats can be allergic to humans. Many cats are allergic to grass, fleas, mites, or dust; but a few of our feline friends are actually allergic to us, too. Often, they are reacting to our perfume, soap, or laundry detergent instead of our skin or hair, though.

• Cats love to be petted. Despite their reputation for aloofness, most cats actually relish physical affection. It's important to pet your cat the right way, however, usually with a single finger around the face or the base of the tail.

• A cat's brain is more complex than a dog's brain. Cats' brains contain about 160 million neurons while dogs come in with just 100 million.  

• Cats have good short-term memories. They put those 160 million neurons to work! In fact, cats' short-term memories help them locate food in the wild.  

• Cats were first domesticated in China. The history of house cats is worth a read, and there's some controversy about exactly which group of people first domesticated cats. But archaeology tells us that at least 5,000 years ago, a Chinese farmer saw a helpful, rodent-controlling kitty and invited him inside for the night. The rest is history.

• Male cats sport barbed penises. The keratinized spines on the feline penis lie flat until the tom gets aroused, then they become rigid. In mating, the spines rake against the interior of the female's vagina, which may be why queen cats are known to scream during the big event.

• Cats have more bones than humans do. The human skeleton contains just 206 bones while the cats' bone structure includes 244 of them. All these bones contribute to a cat's legendary nimbleness.

• A house cat's genome is 95.6 percent tiger. If your kitty acts like a tiny tiger, there's a scientific reason why.

• Cats use their tails to balance. The tail provides counterbalance when running on a narrow platform or jumping on prey. It also serves as a communication device and a mood detector. 

• Not all cats are afraid of water, and some even enjoy swimming. Think about tigers, panthers, and other wild cats. They will take to the rivers or lakes in pursuit of prey. Some house cats will do the same.

• Cats spend up to ⅓ of their waking hours grooming themselves. Unlike dogs that have to be bathed, cats take care of personal cleanliness with their barbed tongues, and they spend a lot of time doing it.

• Female cats can get pregnant at as young as four months old. Cats experience sexual maturity very young, and unless spayed, they will go into heat every 2-3 weeks from spring through early fall. Pregnancy lasts about 63-65 days, meaning a cat can birth a litter of kittens when she's just six months old.

• Cats can make up to 100 different vocal sounds. A dog can make ten, and a human can make 840. Cats use these different sounds to communicate with their humans and with other animals.

• A question-mark shaped tail means, "Want to play with me?" Cats communicate with their tails. An erect tail signals excitement, a swishing tail indicates focus, and a low tail may demonstrate aggression or fear.

• A cat's purr vibrates at a frequency of 25 to 150 hertz. This is the same sound frequency, researchers have found, that improves bone density and promotes healing. Cats purr by using both their laryngeal and diaphragmatic muscles.

• Colonists first imported cats to North America to assist with rodent control. During Colonial times, people kept an astonishing array of pets. Besides horses, dogs, and cats, many American colonists also brought songbirds, squirrels, foxes, and coyotes into their homes and tamed them. 

• The first cat video was recorded in 1894. Early videographers made the film, which they titled "The Boxing Cats," at Thomas Edison's Black Maria Studio in West Orange, N.J.

• The U.S. is home to about 83 million pet cats and 60 million feral ones. The exact numbers vary depending on the source, but one thing is certain: cats outnumber dogs, birds, and pocket pets in homes, making them America's most popular pets.  

Knowing the facts about cats can be fun, but it can also be a great way to help our feline friends stay healthy and happy.