Cats are lactose intolerant. Like most mammals, cats lose the ability to digest dairy after infancy. Feeding milk to a cat can encourage stomach upset and diarrhea.
Dogs with “squashed” faces have more health problems. The structure of the faces of pugs, boxers, and bulldogs makes them more prone to respiratory problems, dental problems, and other health issues.
Cats are capable of about one hundred distinct vocalizations; dogs are capable of about ten.
All Dalmatians are born white. Their spots develop within the first few weeks of life.
Hunting is not an instinctive cat behavior. If a kitten doesn’t learn to hunt from its mother or other cats, it’s unlikely that it ever will.
A dog’s sense of smell is up to one hundred thousand times more sensitive than a human’s. While humans have about five million scent receptors in their noses, a bloodhound has up to three hundred million.
Domestic cats sleep an average of sixteen hours per day. In the wild, big cats that expend lots of energy hunting sleep even longer. Only sloths spend more of their lives asleep.
Dogs’ only sweat glands are between the pads of their feet. They dissipate the majority of their heat by panting, a method far more effective than allowing moisture to evaporate from the skin.
Cats are either lefties or righties. Psychologists at Queen’s University in Belfast discovered that female cats were more likely to favor their right paws, while male cats were more likely to favor their left. As with humans, some cats are ambidextrous, too.
Dogs are one of only two mammal species that have prostate glands. The other species is humans.
Calico cats are almost always female. The gene for coat color is sex-linked, so to express both orange and black coloring, the cat must have two copies of the X chromosome. Rarely, an abnormality produces a male cat with XXY chromosomes and calico coloring; these cats are always sterile.
Dogs aren’t really color-blind. They do see colors, just not as well as humans.
All kittens are born with blue eyes. They begin to change color about two weeks after their eyes open.
Dogs’ wet noses help them smell better. The mucus attracts and “catches” more chemical scent particles in the air.
Most blue-eyed white cats are born deaf—about 65 to 85 percent, says the Cornell College of Veterinary Medicine.
The only dog breed that doesn’t bark is the Basenji. However, Basenjis do make other noises, such as growls, whines, and even yodels.
Cats don’t meow at other cats. They reserve this sound for getting attention (not to mention food) from humans.
Dogs have no clavicles. Their disconnected shoulder blades allow them a greater range of motion for running and jumping.
When cats walk, their left front leg moves in tandem with their left back leg, and their right legs do the same. The only other animals that walk this way are giraffes and camels.
Domestic dogs can breed with wolves. The two animals are still related closely enough that they can mate, producing feral offspring.
The proper name for a group of cats is a clowder. A group of kittens is called a kindle.
It takes eighteen muscles to move a dog’s ear. This specificity of motion helps the dog pinpoint the origins of sounds much faster than a human can.
Both cats’ and dogs’ noses are unique, like human fingerprints. It’s becoming more and more common to take nose prints of dogs in case they’re ever lost or stolen.