A combination of YouTube videos and high-speed digital footage reveals how cats lap liquids so gracefully.
- Cats lap liquids utilizing a sophisticated technique that balances gravity and inertia.
- Felines may drink in this delicate manner to avoid splashing their whiskers.
- Dogs and humans drink using often messier methods that involve gulping and sucking.
The exquisite balance and near gravity-defying grace of cats extends to the way they drink, according to a new Science journal paper that is the first to explain the physics of cat lapping.
An Academy Award-winning film recorded by MIT engineer Doc Edgerton in 1941 showed that a drinking cat curls its tongue backward, like a letter "J" shape, so that the top surface of the tongue barely brushes the surface of liquid. Since that film debuted, however, no one has been able to explain the physics underlying the sophisticated process -- until now.
The authors used YouTube videos in addition to original high-speed digital videos for data collection. An eight-year-old cat named Cutta Cutta, co-author Roman Stocker's beloved pet, starred in most of the original videos, while the selected YouTube ones showed various wild cats, including a cheetah, bobcat, lion, tiger and leopard, drinking.
"A cat's tongue reaches an incredible speed of nearly a meter (just over 3 feet) per second, and is therefore too fast to be captured by the naked eye," co-author Pedro Reis told Discovery News.
"This is why we had to resort to high-speed imaging, often used in science to slow down action that's too fast to be seen otherwise," added Reis, an assistant professor of civil and environmental engineering, as well as mechanical engineering, at MIT.
By slowing down the videos, the researchers determined that after a cat's tongue brushes the surface of a liquid, such as water or milk, a column of the liquid forms between the moving tongue and the liquid's surface. Inertia causes the liquid to stretch upward. Just before gravity brings the liquid back down, the cat draws its tongue in and swallows. All of this happens about four times per second.
The scientists speculate that the delicate feline technique "may be related to keeping whiskers dry, since these play a very important sensory function."
Dogs, on the other hand, are a "lot messier," they said, explaining that a dog morphs its tongue into a cup shape and then fills it with liquid before bringing it, ladle-like, to the mouth.
Our human technique can also be on the messy side, since we generate suction with our mouths, filling our complete cheeks with fluid. Carnivores like cats have incomplete cheeks, which facilitate prey grabbing.
Co-author Jeffrey Aristoff of Princeton University's Department of Mechanical and Aerospace Engineering told Discovery News that he and his team also determined that "large cats drink more slowly than small cats," since the size and speed of the tongue affect the process. The researchers even created a robotic tongue to better study and duplicate the feline technique.
While small cats drink at impressive speeds, rats have an even higher lapping frequency of six to seven times per second. Rats may therefore be the world's fastest drinkers, with cats in the animal top 10.
Professor Steven Vogel at Duke University conducted prior research on animal form and function, particularly in the context of fluid mechanics. He told Discovery News that he fully agrees with the new paper's conclusions.
"I'm just a little embarrassed that I never closely watched our ancient family feline drink, which he does on the bathroom counter each morning as I shave," Vogel said.
Stocker, in fact, was inspired to conduct the new research after admiring the way Cutta Cutta lapped during breakfast.
"Although we also filmed other cats, he has since remained our choice model for both high-speed videos and still photography," Stocker said, adding that "Cutta Cutta" means "many stars," and may have Oscar hopes after his stellar moments in the scientific spotlight.