What makes a wet dog shake off water? The answer surprised scientists completely.

New contenders have emerged for the amusing Ig Nobel Prize – whether in physics or physiology. It seems that American neurobiologists from the Howard Hughes Medical Institute at Harvard Medical School are genuinely in the running – they certainly provided some entertainment.

The researchers studied wet animals – not just dogs, but all those that shake themselves off when wet, vigorously rotating their bodies from side to side. It turns out that many mammals do this: both small and large – from mice to bears. Dogs, of course, are the most illustrative example. They demonstrate the physical essence of the process: the rotation creates a centrifugal force that acts on the water droplets, causing them to fly off their fur.

As determined by scientists from the Georgia Institute of Technology in Atlanta, when shaking off water, mice make about 30 movements per second, cats make 9, while bears and large dogs like St. Bernards do it 4 times per second. This means that the smaller the animal, the faster it shakes. And vice versa.

This raises the question: what exactly prompts animals to shake? Water seems to be the logical answer, as they don’t want to remain wet. However, as it turns out, we are mistaken. Harvard researchers, led by Dawei Zhang, discovered a completely different reason – one that is much deeper. Their recent study was reported by the journal Science – which deemed it worthy and even featured the topic of “wet animals” on its cover.

The study on wet animals was featured on the magazine's cover

Keeping dogs in mind, the scientists prepared genetically modified mice and conducted experiments with them. It was found that the mice sometimes start to shake even when they are not wet. The little creatures reacted not only to water but also to other stimuli – streams of air or even droplets of oil applied to specific spots on their necks. From this, the experimenters made one initial conclusion: touch is responsible for the “shaking process.” When they disabled the Piezo2 gene, which plays a crucial role in touch sensation, the mice stopped shaking. The second conclusion was that something on their necks triggers this process. Presumably, there are some mechanoreceptors located there – that is, nerve endings sensitive to mechanical stimuli. For example, to pressure.

The scientists tested three types of mechanoreceptors – including those that respond to temperature. Ultimately, through trial and error, disabling one type and then another, they discovered that mice always start to shake if C-LTMRs are specifically stimulated. Well, dogs are no different in this regard. They often seem to shake off water after being petted.

My Beagle sometimes shakes for no apparent reason while simply walking on a leash. Maybe something lands on her neck. Or the collar rubs. Now I’ll know.