IF YOU LIVE WITH A DOG, then you are familiar with this sound.
Unlike barks, growls and howls -- dog sounds that easily take center stage -- a dog lapping up water is background, white noise. Dog drinking attracts little attention until you unexpectedly step in a puddle of slopped-over water while wearing socks.
A closer look reveals there is nothing commonplace about how dogs drink. Instead, to ingest liquids, the tongue seems to perform almost acrobatic feats. Slow-motion footage of dogs lapping up water shows that the tongue curls backward to create a spoon shape. The below video from of The Secret Life of Dogs, a Nat Geo WILD special premiering Sunday, August 25, hints at the intricacies of how dogs drink.
From the above clip, it could appear that by curling the tongue backward and filling the spoon-shaped tongue with water, dogs drink by scooping, or spooning, liquids into their mouths. But a paper published by Crompton and Musinsky in Biology Letters in 2011, finds there is more to the story.
While dog tongues do assume a spoon-shaped position while drinking, much of that liquid falls out. Using high-speed and x-ray video recordings of a dog lapping up a colored liquid, instead of clear water, the researchers could see that the tip of the dog's tongue was actually drawing a column of water up into the mouth, and this column of water is what dogs are drinking. This observation is difficult to make from slow-motion videos of dogs drinking clear liquids like water. By taking x-ray video of a dog drinking a dark liquid, in this case a mixture of milk and barium, Crompton and Musinsky could see that dogs draw up liquid by the tip of the tongue, and the tongue then traps previously lapped water onto the roof of the mouth so the dog can bring more water in without losing what it already has.
Ultimately, the researchers found that dogs use the same drinking technique as cats. This might be surprising because dogs make such a mess while drinking, and cats seem to emulate the daintiness of royalty, but dog tongues dive deeper into liquids thereby giving off more spray.
The researchers concluded that dogs and cats share the same basic mechanism for drinking: “adhesion of liquid to the tongue rather than ‘scooping’ by the tongue.” I’ll drink to that.
Images: Dog drinking from water fountain and Sunset Drink via Flicker Creative Commons.
Additional Reading and References
Crompton and Musinsky. 2011. How Dogs Lap: Ingestion and Intraoral Transport in Canis familiaris. Biology Letters 7, 882–884.
Reis et al. 2010. How Cats Lap: Water Uptake by Felis catus. Science 330 1231–1234.
Young. Dogs Do Drink Like Cats After All. Not Exactly Rocket Science. May 24, 2011.