(SCIENCE) An apple falling could be explained by the law of gravity and water staying safely in a swinging bucket by centripetal force. Science is wonderful that way. But what about the simple act of a dog lapping water? You can finally understand how your pooch does it, thanks a few dedicated Harvard and MIT researchers. — Global Animal
ABC, Genelle Wuele
Cat owners can no longer claim their furry friend has superior drinking skills than the average pooch.
Despite their reputation as messy drinkers, dogs use the same gravity-defying lapping technique as cats, US researchers report in the Royal Society Journal Biology Letters.
Last year researchers from the Massachusetts Institute of Technology (MIT) reported that cats bend the top of their tongue to raise liquid in a column to their mouth.
It was thought, however, that dogs formed the bottom of their tongue into a cup shape and scooped water into the floor of their mouth.
Professor Alfred Crompton from Harvard University had previously studied lapping in the American opossum.
Crompton was initially sceptical about the MIT research, but realised the data about cats was “clearly correct.”
“In their Science paper [the MIT researchers] stated that dogs and cats were different,” says Crompton.
“This view was based on a YouTube clip of a dog lapping water.”
So Crompton and colleague Catherine Musinsky decided test the theory using high-speed video and x-ray images of a dog lapping a barium milk broth.
“This showed that the mechanism was the same; dogs do not scoop,” says Crompton.
Just like cats, dogs fold the tip of their tongue backwards so that the top of the tongue penetrates the surface of the liquid.
While water adhering to the top surface of the tongue is pulled upwards to the mouth, water sitting on the bottom side of the tongue spills back down towards the container as the tongue is withdrawn and the jaw closed.
“It is difficult to see the water transport in the YouTube video, but with a barium/milk solution it is clearly visible in x-ray,” he says.
X-rays show it takes three laps to move liquid to the back of the throat. Each time, liquid is trapped against ridges on the dog’s palate to stop the liquid falling out as the tongue is protruded.
“X-ray videos of dog lapping reveal the dexterity which their tongues trap previously lapped aliquots between the rugae on the roof of their mouths and the dorsal surface of the protruding tongue, in order to access the next aliquot without ingesting the previous one,” they write.
Crompton says there are no high-speed x-ray videos of cats, but he suspects that they would use at least two cycles to move the liquid through the oral cavity.
As for the impression of messiness, high speed video of a dog versus a cat shows it all comes down to how far the tip of the animal’s tongue penetrates the liquid.
“The fact that the [dog's] tongue tip penetrates more deeply into the liquid than in cats, and consequently sprays more liquid around as the tongue rapidly withdraws, may give the impression that dogs drink by spooning liquids into their mouths,” they write.
Crompton suspects that the mechanism seen in cats and dogs probably also applies to other animals, including most carnivores, which lack cheeks.
Science in action
Dr Pedro Reis a co-author of the MIT study, says the follow-up study “adds a new element to the story of how animals drink, but also also provides a wonderful anecdote of how science moves forward.”
“As far as lapping goes, this reconciliatory move between felines and dogs is fascinating.”
Colleague Dr Roman Stocker agrees.
“In our study we had made a comment in passing that, based on the information we had … the two animals seemed to employ different mechanisms,” says Stocker.
“[The Harvard researchers] employed a more sophisticated tool … which allowed them to image what the water does within the mouth of the dog.”
“This is a beautiful example of how science progresses by interactions and debate between different groups.”
“Masterfully done and bringing both pets [on par],” he says.