Dog owners are familiar with the unseemly lapping noises that ensue when their thirsty pet meets a bowl of water. The dog is thrusting its tongue into the water, forming a crude cup with it and hauling the liquid back into the muzzle.
Cats, both big and little, are so much classier, according to new research by Pedro M. Reis and Roman Stocker of the Massachusetts Institute of Technology, joined by Sunghwan Jung of the Virginia Polytechnic Institute and Jeffrey M. Aristoff of Princeton.
Writing in the Thursday issue of Science, the four engineers report that the cats lapping method depends on its instinctive ability to calculate the point at which gravitational force would overcome inertia and cause the water to fall.
What happens is that the cat darts its tongue, curving the upper side downward so that the tip lightly touches the surface of the water.
The tongue is then pulled upward at high speed, drawing a column of water behind it.
Just at the moment that gravity finally overcomes the rush of the water and starts to pull the column down snap! The cats jaws have closed over the jet of water and swallowed it.
The cat laps four times a second too fast for the human eye to see anything but a blur and its tongue moves at a speed of one meter per second.
Being engineers, the cat-lapping team next tested its findings with a machine that mimicked a cats tongue, using a glass disk at the end of a piston to serve as the tip. After calculating things like the Froude number and the aspect ratio, they were able to figure out how fast a cat should lap to get the greatest amount of water into its mouth. The cats, it turns out, were way ahead of them they lap at just that speed.
To the scientific mind, the next obvious question is whether bigger cats should lap at different speeds.
The engineers worked out a formula: the lapping frequency should be the weight of the cat species, raised to the power of minus one-sixth and multiplied by 4.6. They then made friends with a curator at Zoo New England, the nonprofit group that operates the Franklin Park Zoo in Boston and the Stone Zoo in Stoneham, Mass., who let them videotape his big cats. Lions, leopards, jaguars and ocelots turned out to lap at the speeds predicted by the engineers.
