How Cats Drink

High-speed video footage of household pets feeding has revealed the exquisite balance of forces at work when a cat laps a bowl of milk.
While dogs use their tongues to scoop up liquid, the cat's tongue makes only the briefest contact with the liquid's surface, before quickly retracting to pull a thin column of milk into the mouth.
The act of lapping is judged so perfectly the cat catches the milk in its mouth before gravity overcomes the liquid's inertia inducing it to fall back into the bowl.
The unusual study began when Roman Stocker, an expert in fluid mechanics at MIT in Cambridge, Massachusetts, became fascinated by watching his eight-year-old cat, Cutta Cutta, drinking at breakfast time.
Without funding or turning to his own graduate students for help, Stocker assembled a diverse team of experts to investigate the commonplace mystery of how cat lapping works.
Writing in the US journal Science, the researchers describe how they analysed video footage of domestic and big cats and found they all lapped in the same way. As the cat's tongue is extended it curls under so that the top surface of the tip makes contact, but does not break the surface of the fluid. Some liquid sticks to the tongue and rises in a column as the cat retracts it. The liquid is drawn upwards by the drop in pressure created by the fast moving tongue.
High-speed video revealed that domestic cats average about four laps per second, with each lap bringing 0.1 millilitres of liquid into the mouth. Larger cats draw up thicker columns of liquid and so can afford to lap more slowly.
"The amount of liquid available for the cat to capture each time it closes its mouth depends on the size and speed of the tongue. Our research suggests that the cat chooses the speed in order to maximise the amount of liquid ingested per lap," said Jeffrey Aristoff, a co-author on the study. "Cats are smarter than people think, at least when it comes to hydrodynamics."
The team went built a mechanical model of a cat's tongue that could move up and down over a bowl of water, allowing them to explore the mechanism underpinning lapping.
The cat is not the first animal known to exploit a fine balance between inertia and gravity. The Basilisk lizard can run on water by slapping the surface with its feet to create air pockets that prevent it sinking, providing it moves fast enough.