How a Dog Drinks

Late last year, researchers from the Massachusetts Institute of Technology used high-speed photography to describe the elegant way in which cats lap up liquid with the tip of the tongue, seemingly defying gravity. Dogs, on the other hand, form a cup with the tongue and scoop up liquid, the researchers said, spilling quite a bit of it.

Not so, according to Alfred Crompton, a zoologist at Harvard, and Catherine Musinsky, his assistant, who used high-speed light videos and X-ray videos to demonstrate that dogs and cats actually use the same mechanism to drink. They report their findings in the current issue of the journal Biology Letters.

“Dogs are just a little more exuberant and messy in their drinking, so it looks like it’s being scooped up,” Dr. Crompton said. “But they do it the same way as cats.”

Both animals reach into liquids with the tips of their tongues, pulling up a long column. Before the liquid drops back down, they open their mouths and pull it in.

But the dog tongue tip penetrates the liquid a little more deeply than the cat tongue, causing a messy spray around the tongue during withdrawal, Dr. Crompton said. This gives the false impression that dogs use a scooping motion.

“The video shows that all the liquid that was so-called being ‘scooped up’ falls right back out,” he said.

The test subject in the study was Dr. Crompton’s dog, Mathilda. Once the liquid was in her mouth, they saw that it was held in ridges called rugae on the roof of the mouth before it continued down her throat. This intermediate location for the liquid allows Mathilda, and other dogs, to lap continuously and pull in another column of liquid without losing the previous one.