Lap it up, fur ball!

Yesterday’s neuro words for nerds term was prehension, so I thought it would be fun to look at how cats lap up water and milk. This article discusses the results presented in: Reis PM, Jung S, Aristoff JM, Stocker R. How cats lap: Water uptake by Felis catus. Science 2010;330:1231-4.

There are two primary methods by which vertebrates drink liquid — suction and lapping. Vertebrates with complete lips, such as horses, pigs, and sheep, use suction and the tongue to move the liquid into the mouth. Vertebrates with incomplete lips, including most carnivores, are unable to seal their mouth enough to produce the suction required to drink and therefore must rely on their tongue to lap up liquids.

Dogs have been shown to drink liquid by curling the tip of the tongue downward (ventrally) in a ladle-like fashion, submerging it under the surface, and then scooping liquid into the mouth. Until recently, the theory was that cats lapped up liquids similar to dogs. But one morning while having breakfast, biophysicist Roman Stocker was watching his cat, Cutta Cutta, lap water from a bowl and started to wonder whether this assumption was correct.

Want to know how fast your cat laps water? Take your cat’s weight in kilograms raised to the negative 1/6th power and multiply by 4.6.

He and three other MIT researchers used high-speed video to record Cutta Cutta and nine other cats lapping water. They found that cats drink using a much more interesting and complex process from a bioengineering point of view. Their videos showed that the tip of the tongue (which is smooth) curves downward (ventrally) like a dog, but rather than submerging the tongue and using it as a ladle, cats only touch the surface of the liquid. As the tongue pulls back into the mouth, liquid adhered to it forms a column of liquid that is drawn upward toward the mouth. The liquid is subject to two forces: inertia pulling the liquid in the same direction of tongue movement and gravity pulling the liquid back down. Eventually, gravity overcomes inertia, and the liquid falls back. Just as the fluid starts to fall back, the cat’s mouth closes around the top of the column pinching off some of the liquid that the cat swallows (See chronological image). The recorded lapping frequency for these ten cats was 3.5 ± 0.4 laps per second, and one lap pulled in 0.14 ± 0.04 mL ( ≅ 3/100 tsp ).  The researchers then videotaped several larger cat species at the Franklin Park Zoo and Stone Zoo in Boston and found that lions, leopards, jaguars, and ocelots lapped at a frequency similar, but slightly lower than, their predicted calculations. The larger the species of cat, the slower the lapping.

Check out this article from NPR, Pet Physics: The Uncanny Lapping of Cats, which includes slow-motion, high-speed video of a dog lapping up water and a cat lapping up milk.

Photo credit: Cat lapping milk. Irina Kozorog/Shutterstock