Dogs and cats see in black and white: Their eyes, like ours, contain rods and cones—structures that process black and white and color—so we know they can see some hues. Dogs likely process blues and greens (but not reds), and cats see all colors of the spectrum.
Cats and dogs eat grass when they’re sick: Studies have shown that this is normal behavior that has no correlation with illness. The animals do not become ill (though cats may cough up hair balls, which is healthy) unless the grass contains toxic materials.
One human year equals seven dog years: The speed at which a dog ages depends on its breed and genetic makeup, not a general formula. Large breeds tend to grow up faster than smaller ones. A seven-year-old Chihuahua? Forty-four. A Great Dane? Fifty-six.
Cats always land on their feet: Thanks to their skeletal structure and internal equilibrium mechanisms, felines can right their bodies in midair and land feet first most of the time. When they fall from very low or very high elevations, all bets are off.
Images courtesy (in order): (1) Flickr/felinest, (2) Flickr/ajball90, (3) Flickr/normanack, (4) Flickr/Ali Smiles :)