In this article

1. Why a wet coat is worth shaking off
2. How fast dogs shake, and why small dogs shake faster
3. What sets off a shake
4. Why dogs drink so messily
5. Drying your dog after a wet walk
6. Water bowls, and when thirst needs a vet

Your dog bounds out of the river, trots straight over to you and plants all four feet. You know what comes next. A second later you are wearing a good share of the river, and your dog looks thoroughly pleased with themselves.

Back home, the same dog drinks from their bowl and leaves a puddle across the kitchen floor. Both habits can look like bad manners, but both are neat pieces of physics that scientists have filmed at high speed. Here is what they found, and what it means for towels, water bowls and wet winter walks.

Why a wet coat is worth shaking off

Water in fur is more than a nuisance. Engineers at the Georgia Institute of Technology in the United States, who studied how mammals shake dry, point out that water conducts heat about 25 times better than air, so a soggy coat insulates poorly and a wet animal loses heat fast¹.

Evaporation is costly too. The team worked out that a wet 27 kg dog carrying about 450 g of water in its fur (60 pounds and one pound, in the paper's own units) would use 20 per cent of its daily calorie intake just to air-dry¹. That figure is a calculation rather than a measurement, but the authors' point is plain: for land animals, staying dry in cold weather is a matter of survival¹.

How fast dogs shake, and why small dogs shake faster

The Georgia Tech team measured the shakes of 33 animals, 16 species and five dog breeds, from mice to bears¹. The overall pattern was clear: the smaller the animal, the faster it tends to shake, as these figures from the study show¹.

Animal	Weight	Shakes a second
Mouse	0.03 kg	29
Chihuahua	2.5 kg	6.8
Siberian husky	10.9 kg	5.8
Labrador retriever	28.1 kg	4.5
Brown bear	About 260 kg	4.0

Why does size matter? Drops cling to hair by surface tension, and a shake flings them off by whipping the coat round fast enough to throw them clear. The animals in the study generated forces of 10 to 70 times gravity to shed their drops, and a smaller body has to twist faster to reach that force¹. If a mouse shook at a dog's pace, the researchers calculated, it would produce only about the pull of ordinary gravity and stay just as wet¹.

The loose-skin trick

Dogs have another advantage: loose skin. When the team taped a marker to the backs of Labradors, the marker swung round to about 90 degrees from upright, while the researchers worked out that the backbone itself turned only about 30. The loose skin roughly tripled the swing, and they calculated that a tight-skinned animal shaking at the same rate would stay almost as wet as before¹.

Even so, a shake never gets a dog bone dry. In the team's tests with wet deer fur on a spinning rig, shaking at these speeds removed about 70 per cent of the water, and however fast the fur was spun, about 30 per cent stayed put¹. It is still a bargain: by their sums, a shake uses between a ten-thousandth and a thousandth of the energy it would take to evaporate the same water¹.

What sets off a shake

Why should a few drops on the back set off a full-body shimmy? A 2024 study in mice offers a clue. Researchers at Harvard Medical School found that swimming, a spray of water or a drop of water or oil on the back of the neck all made mice shake⁶.

The trigger turned out to be touch. Mice bred to lack a key touch-sensing protein in their body's sensory nerves barely shook after a dip⁶. Nerves in hairy skin that respond to gentle, lingering touch play a part: switching them on with light made the mice shake, and removing most of them roughly halved the shaking after a drop of oil⁶.

The authors note that the back and neck are hard for an animal to reach by licking or grooming, which is where a shake comes in⁶. Dogs were not in the study, so it is a clue to how they work, not proof.

Why dogs drink so messily

Now to the water bowl. Dogs lap because they have incomplete cheeks and cannot suck, as a Virginia Tech team put it after filming 19 dogs drinking³. With no seal to draw water in, the tongue has to fetch it³. Here is one lap, slowed right down.

One lap, step by step

1. Reach downThe tongue stretches out and curls backwards into a ladle shape³
2. Hit the waterThe curled tongue strikes the surface, making a splash³
3. Pull upThe tongue whips back up at one to four times the pull of gravity, drawing a column of water with it³
4. BiteThe jaws close at about the moment the column would break, catching the water³
5. RepeatIn an X-ray study of one dog, each mouthful took at least three laps to travel through the mouth⁴

Ladle or sticky tongue?

That curled tongue looks like a spoon, and it had been suggested that dogs scoop water up with it. X-ray video says otherwise. In a 2011 study, researchers at Harvard's Museum of Comparative Zoology filmed one dog lapping, including a milk and barium mixture that shows up on X-ray. Most of the liquid in the spoon fell out as the tongue rose. What reached the mouth was mainly liquid clinging to the tongue's upper surface, which faces down into the bowl when the tip curls back⁴.

The 2015 Virginia Tech study agrees that dogs do not scoop, but argues the curl still earns its place. In lab tests where rods were pulled out of water to mimic a tongue, wider rods and faster pulls lifted more water, which suggests a dog curls its tongue to make it wider and pull up more per lap³. The scooped water might even help by spilling round the tongue to feed the column, an idea the authors say needs testing³.

Cats lap too, but more daintily. A cat's tongue rises at about one to two times gravity and slows as it enters the mouth, while a dog's accelerates harder³. A dog's tongue also dips deeper into the water than a cat's, and so sprays more liquid around⁴.

Where the mess comes from

The Virginia Tech team names the culprits. A dog's tongue meets the water over a large area, plunges below the surface and then shoots upwards fast. Not all the water it moves joins the column: some splashes sideways, and the water sitting in the ladle tends to be tossed out to either side of the mouth³. The mess, they suggest, may be a by-product of a lapping style that pulls up more water per lap³, which is a fair excuse for a mat under the bowl.

Drying your dog after a wet walk

The physics gives you a simple plan: let the shake go first, then finish with a towel, since a shake leaves some water behind however hard your dog tries¹. The PDSA says a pet that dries off after getting wet is unlikely to get cold, but one that stays wet and gets cold is at risk of hypothermia, especially on a cold day, after very cold water, or if they stop moving around².

Water bowls, and when thirst needs a vet

Back in the kitchen, the splashing is normal and worth living with, and an old towel under the bowl helps. What matters more is that the bowl is never empty: the PDSA's advice is to always allow your dog fresh drinking water, and never to restrict it to deal with a drinking problem⁵. How much is normal depends on size, health and activity, so ask your vet what is right for yours⁵.

Do keep half an eye on how often you refill it, though. The PDSA lists the signs to look for: emptying the bowl faster than usual, drinking from taps, puddles or streams more than usual, and weeing more often, in larger amounts or in the house. Exercise and hot weather can raise thirst for a while, but if you think your dog is drinking or weeing more than normal, the PDSA says to contact your vet⁵.

So the next time your dog soaks your jeans or floods the kitchen floor, you are watching a small physics demonstration. Stand back, reach for the towel, and let them get on with it.

Sources and further reading7 sources

The small numbers in the article link to the source behind each fact. Sources open on their own websites.

1. Wet mammals shake at tuned frequencies to dryJournal of the Royal Society Interface
2. Hypothermia in PetsPDSA
3. Dogs lap using acceleration-driven open pumpingProceedings of the National Academy of Sciences (PNAS)
4. How dogs lap: ingestion and intraoral transport in Canis familiarisBiology Letters
5. Why is my dog drinking lots of water and weeing more than usual?PDSA
6. C-LTMRs evoke wet dog shakes via the spinoparabrachial pathwayScience
7. Water safetyPDSA