54 | New Scientist | 20 February 2021Shake it off
Why do dogs like to shake
themselves dry beside people,
rather than doing this as soon
as they get out of the water?Anna Butcher
Brookton, Western Australia
Observations on our farm have
almost convinced me that dogs
deliberately choose to shake
themselves dry beside a person.
This seems to be the way that our
kelpie sheepdogs get even with
me after they have been washed.
It takes a lot of hard work
for them to garner the most
delightful, cultured odour
from all manner of dead
things from around the farm.
Then, in a short space of
time, all their hard work is for
naught, when they have their
six-weekly wash and pedicure.
However, if they have chosen
to jump into a water trough to
cool down or get a drink and
are sopping wet, they seldom
shake themselves.Chris Warman
Hinderwell, North Yorkshire, UK
They shake themselves off next
to you because they love you.
Dogs are social animals and thebonds between pack members
are constantly renewed by
little ceremonies.
Even if your dog has only
been away for a few minutes,
when it returns, it will be strongly
motivated to greet you and
will waste no time in doing so.
Drying off can wait, and the
dog won’t see the connection
between shaking itself off and
what might seem to you like a
heartless snub.
Just be thankful it is only
water you are being sprayed with.Want to send us a question or answer?
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STEPHAN^ SCHRAMM/ALAMYMike Follows
Sutton Coldfield,
West Midlands, UK
Dogs and other animals dry
themselves as a survival strategy.
A wet dog will chill quickly as
water evaporates. The water also
displaces the air trapped in layers
of fur that acts as an insulator.
It is estimated that a dog would
use up about 15 per cent of its
normal daily food intake getting
warm again each time it went for
a dip without shaking itself dry.
This drying method isn’t
specific to dogs. Researchers at the
Georgia Institute of Technology
in Atlanta filmed a range of furry
creatures and discovered that
the smaller the animal, the faster
they spin themselves in order to
shake off water.Mice spin at about 30 times
a second and cats at nine times
a second, whereas a Labrador
retriever twists its body from
side to side at a more leisurely
four cycles per second.
Dogs don’t set out to soak
their owners when they shake
themselves dry. They are social
animals so probably prefer to
shake themselves in the company
of their packs than on their own.David Muir
Edinburgh, UK
A dog’s backbone can rotate about
30 degrees in either direction.
When you combine that with the
fact that most dog breeds have
very loose skin, the fur can flick
around 90 degrees each way. With
the sharp change in rotation, thewhip effect can get rid of 60 to
70 per cent of the water in a wet
dog’s coat in a few seconds.
With the whip-flick motion
of the skin and hair, dogs
instinctively close their eyes to
protect them. The ancestors of
today’s domestic dogs would
have been vulnerable to predation
during these few seconds.
This risk may not have been
particularly high, but what better
way for a dog to minimise this
than by sidling up to another pack
member and using their vigilant
eyes and proximity to guard itself
against potential predators. In the
case of pet dogs, that pack
member is human.Chris Daniel
Glan Conwy, Conwy, UK
Accounts of dogs drenching
their owners by shaking off water
next to them may be a form of
confirmation bias. People may
not notice or remember other
times when they were out of
range while their dog did this.
If this doesn’t convince most
owners, they can at least marvel at
the physics of the action. It starts
with the head rotating from side
to side at around four shakes per
second. The oscillation travels
down the body until the pelvis is
rotating in the opposite direction
to the shoulders. The centripetal
force caused by rotations of
almost 90 degrees each way
causes the water to fly off in an
impressive spiral spray, removing
the majority of it from the fur.
With a final shake of the tail, the
dog is ready for its next adventure.Bubble trouble
In carbonated water, larger
bubbles oscillate as they float
upwards. What causes this, and
why is it only big bubbles?Amir Pahlavan
Yale University, Connecticut, US
When you pour sparkling waterThis week’s new questions
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can’t I bend a sunbeam with a magnet? Martin Copsey,
Peterborough, Cambridgeshire, UKMale lions will kill the cubs
of other males, so how do
their recognise their own?“ Observations on our
farm have almost
convinced me that
dogs deliberately
shake themselves
dry beside a person”