I’m sure you have noticed when your dog drinks water, it makes a mess. This mess is worse with dogs with saggy lips like bulldogs, bloodhounds, Mastiffs, St. Bernards and Newfoundlands.
Cats on the other hand have much better manners and the water is not typically spilled on the floor around their drinking bowls.
“Cats rule, dogs drool” — at least when it comes to drinking water, scientists say. Neither dogs nor cats have large cheeks to create suction and form a seal when drinking.
Humans, horses, sheep and pigs all have large cheeks that can create suction to drink, but not dogs and cats.
If we were out in the wilderness and needed a drink from a creek or lake but were unable to use our hands to drink, we would merely place our mouth on the water surface and suck the water into our mouths and our cheeks would form a seal.
Dogs’ and cats’ cheeks do not extend forward enough to create suction. Drinking is more of an anatomical challenge for them than for us.
Dogs use their tongues like a ladle or a spoon to scoop liquid into their mouths. They move some water with the bottom of their tongues, but most of this falls off as the tongue retracts.
If it’s acting as a spoon, it’s not a very good one. Thankfully, the tip of the tongue also draws up a column of water, and before this collapses, the dog closes its mouth around it.
Cats’ drinking is much more complicated. When cats lap up liquids, they extend their tongues straight down toward the bowl with the tip of the tongue curled backward. The top of their tongues touches the liquid first.
But recent high-speed videos made by MIT, Virginia Tech and Princeton researchers reveal that the top of the cat’s tongue is the only surface to touch the liquid.
Cats, unlike dogs, don’t dip their tongues into the liquid like ladles or spoons.
“The cat’s lapping mechanism is far more subtle and elegant,” according to MIT researchers.
The tip of the tongue just barely touches the surface of the liquid before the cat draws its tongue back up.
As it does so, a column of liquid forms between the moving tongue and the liquid’s surface. The cat then closes its mouth, pinching off the top of the column for a nice drink, while keeping its chin dry.
When the cat’s tongue touches the liquid surface, some of the liquid sticks to it through liquid adhesion, much as water adheres to a human palm when it touches the surface of a pool.
“The cat draws its tongue back up so rapidly that for a fraction of a second, inertia — the tendency of the moving liquid to continue following the tongue — overcomes gravity, which is pulling the liquid back down toward the bowl,” MIT researchers wrote.
“The cat instinctively knows just when this delicate balance will change, and it closes its mouth in the instant before gravity overtakes inertia. If the cat hesitated, the column would break, the liquid would fall back into the bowl, and the tongue would come up empty.”
While the domestic cat averages about four laps per second, the big cats, such as tigers, know to slow down. Because their tongues are larger, they lap more slowly to achieve the same balance of gravity and inertia, according to the journal Science.
MIT researchers are trying to incorporate the cat tongue movement into the development of more flexible robotic systems.
But the work could be important in the field of soft robotics, which often models itself upon boneless but dexterous structures like elephant trunks, octopus arms — or cat tongues.