Mystery of how cats lap is revealed

By Rebecca Morelle
Science reporter, BBC News


It is a mystery that has long puzzled cat lovers: exactly how do their feline companions lap up liquids so elegantly?

Now, with the help of high-speed cameras and a pet cat, a team of researchers think they have the answer.

They found that cats use their tongues to delicately draw up water without breaking the surface of the liquid.

The scientists, who published their study in the journal Science, say this differs from dogs, who employ a messy scooping action to quench their thirst.

The team thinks cats may have adopted this more complex but neater approach because it means they are less likely to be splashed with water as they drink.

Feline physics

Dr Roman Stocker, a biophysicist from the Massachusetts Institute of Technology, US, was inspired to investigate the physics of cat laps after watching his own pet Cutta Cutta as it drank.

"I realised there was an interesting biomechanics problem hidden behind that very simple action. The project then snowballed from there," he said.

Working with researchers from Virginia Polytechnic Institute and Princeton University, Dr Stocker trained a high-speed camera on his cat.

While humans and animals such as sheep or horses use suction to draw liquid upwards, and dogs curl their tongue into a cup-like shape to ladle liquid in, the footage revealed that cats use a more subtle mechanism to drink.

Image caption,
The study was inspired by Cutta Cutta the cat

The scientists found that the tip of the cat's tongue curls backwards, not forwards, as it darts down towards its bowl.

Then, instead of penetrating the surface of the liquid, the tongue just lightly touches it.

Dr Stocker explains: "The fluid comes in contact with the tongue and sticks to it, then the action of the tongue being drawn upwards very rapidly creates a liquid column.

"Then, by closing its jaw, the cat captures part of that liquid."

Surprisingly, the researchers also found that the tiny hairs on the tongue, which were once thought to help cats lap, were not involved at all in the process.

To look at the mechanism in even more detail, the team created a robotic cat tongue. They found the process was down to an interplay between two forces: inertia and gravity.

Dr Stocker explained: "The creation of the water column is driven by the force inertia - the tendency of the liquid, once in motion, to keep going.

"The water column initially becomes larger in length and in volume, but at some point the weight of the column itself overcomes these inertial forces, and gravity causes the column to collapse back into the bowl."

Because of this, the cat's timing when lapping is crucial.

"There is a time when the volume of a column is at a maximum, which is at the time at which the cat closes its jaw," Dr Stocker said.

Cats vs dogs

By studying zoo animals and YouTube footage, the researchers also discovered that big cats such as tigers, leopards and cheetahs also used the same mechanism as their domestic cousins.

Image caption,
Dogs use their tongues to drink in a different way to cats

But Dr Stocker and his colleagues are not sure why felines have developed this sophisticated drinking mechanism, but they suspect it could be down to their dislike of water.

He explained: "The lapping mechanism of cats seems to be a lot cleaner compared with dogs, which is much more vigorous and produces more splash.

"One speculation is the face of the cat, and particularly the region around the nose and the whiskers, is extremely sensitive, therefore the cat might want to try and keep that as dry as possible."

"I would say cats know more about fluid mechanics than dogs," he added.

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