US researchers explain how cats lap liquids with elegance

WASHINGTON (AFP) – US researchers on Thursday unveiled the secret of how cats lap water or milk with such elegance, a phenomenon that happens so fast it cannot be followed by human eyes.
Cats are among the many species that, unlike humans, cannot close their mouths and create suction.
With help from from high-speed video taken of a felines lapping liquid, researchers at the Massachusetts Institute of Technology (MIT) and Princeton University found that household cats and larger felines like tigers balance gravity and inertia as they imbibe liquids.

The research will appear in the November 12 issue of the journal Science.
Scientists already knew that when cats insert their tongue into a bowl of liquid, the top surface of the tongue touches the liquid first, then the tip curves like a letter J to form a sort of ladle.
This was first observed by an MIT engineer, who filmed a cat lapping liquid in 1940.

However by studying the images researchers have now determined that there is no ladling effect, but instead the cat's tongue darts in and out so quickly that the action forms a column of liquid.
"Cats, unlike dogs, aren't dipping their tongues into the liquid like ladles after all," read a statement from the MIT Department of Civil and Environmental Engineering.
Instead, the smooth tip of cat's tongue "barely brushes the surface of the liquid before the cat rapidly draws its tongue back up.
"As it does so, a column of milk 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."
The liquid column "is created by a delicate balance between gravity, which pulls the liquid back to the bowl, and inertia, which in physics, refers to the tendency of the liquid or any matter, to continue moving in a direction unless another force interferes."

The cat "instinctively knows just how quickly to lap in order to balance these two forces, and just when to close its mouth. If it waits another fraction of a second, the force of gravity will overtake inertia, causing the column to break, the liquid to fall back into the bowl, and the cat's tongue to come up empty."
Cats average about four laps per second, with each lap bringing in about 0.1 milliliters of liquid, the researchers said, adding that larger felines lap at a slower pace.