Physics of drinking dogs revealed

From BBC
Cats and dogs use same technique to lap up liquid
By Rebecca Morelle

VIDEOS AT http://www.bbc.co.uk/news/science-environment-13523366

Cats and dogs have at last got something in common - at least when it comes to quenching their thirst.

Until now, it was thought that they used remarkably different techniques to drink: for felines, an elegant lap; for canines, a messy scoop.

But scientists have shown the domestic rivals both use the same subtle balance between inertia and gravity to draw liquid into their mouths.

The research is published in the journal Biology Letters.
Cats v dogs

In 2010, a study in the journal Science, revealed the physics behind how cats lap.

Using high-speed cameras, scientists filmed Cutta Cutta the cat, who belonged to lead author Roman Stocker from the US Massachusetts Institute of Technology, as she drank.

They found that as her tongue came into contact with the surface of the water, the liquid stuck to it. Then, as she drew her tongue back towards her mouth, it created a water column, thanks to inertia, which means liquid has a tendency to continue moving in the direction it is being pulled.

High-speed cameras trained on Cutta Cutta the cat revealed how felines lap up liquid (footage courtesy of Pedro Reis, Sunghwan Jung, Jeffrey Aristoff and Roman Stocker)

Finally, when the column was at its peak - and before gravity forced it back down - she snapped her jaw shut, capturing the liquid.

While cats were heralded for their grasp of fluid mechanics, the authors suggested that thirsty dogs simply scooped up water by using their mobile tongues as ladles.

But now, dog-owning scientist Professor Alfred Crompton, from Harvard University, working with Catherine Musinsky who is also from Harvard, has revealed that canines are just as sophisticated as cats when it comes to having a drink.

He said: "We felt we should stand up for the dogs and write this paper."

To discover in precise detail how dogs drink, he trained a high-speed camera as well as an X-ray camera onto his dog Matilda.

He said: "At first, it looked like dogs were scooping, but that is a snare and a delusion."

Messy drinkers
In fact, the footage revealed that any water caught up in her spoon-shaped tongue quickly dropped out before hitting her mouth.

Instead, just like a cat, water was adhering to the back of Matilda's tongue to create a water column. And then, just as the water was about to fall back towards the bowl, she was snapping her mouth shut to get her drink

The only difference between cats and dogs was the fact that the cats tended not to break the surface of the water with their tongues, while dogs opted to penetrate their tongues deep into the bowl.

Professor Crompton said this may be down to a difference in grooming.

He explained: "Cats are just a little more particular about the mess they make. They always like to be neat and clean and to tidy themselves up. They curl their tongue backwards and lay it onto the surface of liquid without penetrating it, so they don't make a mess.

"Dogs on the other hand are a bit more exuberant - they don't worry about spreading the liquid around and making a mess."

The surprising similarity between cats and dogs reveals that a common ancestor would have used this technique too, Professor Crompton added