An expert on dog drinking behaviour, Stocker. (ref 1), says that vertebrates are divided into two classes of animals. There are those with complete cheeks, for example, humans, sheep, horses and pigs, and those with incomplete cheeks, for example most carnivores. Animals such as dogs that have incomplete cheeks use their jaws extensively and most significantly to catch prey, but they cannot create a vacuum with their mouth to drink.

How dogs drink

Slow motion studies confirm that “dogs drink by extending their tongue out from the mouth, morphing it into a cup. As their tongue enters the water, the 'cup' fills with liquid and they then bring it to the mouth.” (ref 1) What this explanation fails to mention is that this is actually an inverse (upside down) cup!

A quick scan of the net comes up with this Dog Drinking water video , it shows a black dog drinking water in slow motion extending its tongue, making the inverse cup and dragging its tongue quickly back into its mouth before gravity acts.

How cats drink

Cats have a similar issue with their ‘incomplete cheek’ but rather than using a cup, they bend the upper side of their tongue under so that the top surface lightly touches the liquid. Then by withdrawing the tongue rapidly, water is drawn upwards in a liquid column. All they need to do is close their jaw to secure the liquid before gravity disrupts the column.

A good video of this motion at 600 frames per second can be seen at Cat Drinking milk video. It appears that the cats tongue motion is really like an inverted half cup, similar to the dogs, however the motion is much faster, and ‘neater’. One clip goes further to state that the main aid to this method is thousands of microscopic ridges on the cats tongue help hold the water in place longer as it withdraws its tongue.

It is thought that this cleaner action may have evolved to reduce splashing, which keeps whiskers dry for their very important sensory action. But because of the reduced volume of water that this action generates compared to the dogs method, cats have to lick at up to four times per second and a tongue speed of one metre per second.

Size of cat related to lapping speed.

Further to this analysis researches came up with a formula that shows that large cats lap more slowly. After reviewing video of eight species of large cat at New England zoo it was found that the cats actually have adjusted the lapping frequency based on hydrodynamics (physics of water) and the size of their tongues to achieve optimum water intake.

So next time you look at a dog or cat drinking water and wonder why they slurp so much, spare a thought of how long it took for each species evolution such efficient methods of gaining the indispensible water resource.

Reference

Ref 1  http://www.abc.net.au/science/articles/2010/11/12/3064918.htm

Article by Bruce Dwyer. If you wish to use any of this information please refer to the article as a reference and provide a live link to http://www.dogwalkersmelbourne.com.au