Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved November 9, 2015 (received for review July 27, 2015)
Significance
Cats and dogs are assumed to drink similarly, but little is known about the actual physical mechanisms that dogs use to transport fluids when lapping. We observed the drinking behavior of a wide range of dogs across breeds and body size, and used physical experiments to mimic the motion of a dog’s tongue as it exits the water. Dogs accelerate the tongue upward more quickly than do cats, and then time their bite to coincide with the pinch-off of the column. The everyday experience of dogs as messy drinkers results from the backward curl of the tongue, which increases the size of the water column and thus enables dogs to drink more per lap than with a straight tongue.
Abstract
Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog’s tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in 19 dogs and used the results to generate a physical model of the tongue’s interaction with the air–fluid interface. These experiments help to explain how dogs exploit the fluid dynamics of the generated column. The results demonstrate that effects of acceleration govern lapping frequency, which suggests that dogs curl the tongue to create a larger liquid column. Comparing lapping in dogs and cats reveals that, despite similar morphology, these carnivores lap in different physical regimes: an unsteady inertial regime for dogs and steady inertial regime for cats.
Footnotes
- ↵1To whom correspondence should be addressed. Email: sunnyjsh{at}vt.edu.
Author contributions: S.G., J.J.S., P.P.V., and S.J. designed research; S.G., J.J.S., P.P.V., and S.J. performed research; S.G. and S.J. analyzed data; and S.G., J.J.S., P.P.V., and S.J. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1514842112/-/DCSupplemental.
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