Hey kitty, dogs drink like cats

Physics of lapping crosses species boundary

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There may be some outraged sofa clawing and houseplant destruction over this, but a complex system of lapping liquids described last year for cats turns out to be the way dogs drink too. High-speed video using X-rays now shows that dogs get liquids into their mouths by relying on the way liquid adheres to their tongues and the inertia of liquid columns, says evolutionary biologist A.W. Crompton of Harvard University. Dogs plunge their tongues into liquid and, like cats, swiftly pull up a little column of it through adhesion. Before gravity overcomes the column’s inertia and the liquid splashes down into the bowl again, the dogs snatch a sip, Crompton and Catherine Musinsky, also of Harvard, report in an upcoming Biology Letters. That’s basically the same mechanism a team reported admiringly in Science last year when describing the way cats lap liquids . “We surely were surprised when we first saw their results,” says Roman Stocker of MIT, a coauthor of the cat study. The feline member of the cat-drinking research team was a precise lapper, just tapping his tongue against the surface of a liquid instead of sloshing into it. But after watching a YouTube video of a dog drinking, Stocker and his colleagues speculated that the splashy laps of dogs appeared to rely on a different technique. On the video, the canine tongue curled down into the water and caught a little pool within its curve. Dogs, the researchers suspected, were nothing more than scoopers. Not so, Crompton says. Full observations show that any water scooped by the dog’s tongue falls out as the tongue moves back into the mouth. As in cats, it’s the top of the liquid column that’s the real drink. “Cats are just a little neater,” Crompton says. Crompton and Musinsky’s X-rays also add a new chapter to the story of lapping by detailing how liquid gets from the front of the tongue to the swallowing point. The tongue traps the water against the ridged roof of the mouth. As the tongue moves out again and again for subsequent laps, captured bits of liquid travel back. A particular bit of captured liquid may need three tongue extensions to get swallowed. Cats probably do this too, Crompton says. Cat study coauthor Jeffrey Aristoff, at Princeton University, notes that the oral cavities are similar for cats and dogs. So the creatures’ similar lapping habits shouldn’t be that much of a shock.

VISIBLE DRINK

X-rays of a Portuguese water dog drinking barium-labeled milk allowed researchers a glimpse of how the tongue traps the water from a lap against the ridged roof of the mouth.
Credit: A.W. Crompton and C. Muskinsky/Harvard Univ.

Susan Milius

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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