Cats often sleep on their left to spot threats faster. Their brain processes danger more efficiently this way.
Many cats appear to favor resting on their left side, according to a recent study conducted by an international team of researchers. The group reviewed several hundred YouTube videos featuring cats in side-sleeping positions. They propose that this side-sleeping preference may have evolved as a survival mechanism, enhancing the animal’s ability to hunt or flee quickly after waking.
The study was carried out by scientists from the University of Bari Aldo Moro (Italy), Ruhr University Bochum, Medical School Hamburg, and collaborators from Germany, Canada, Switzerland, and Turkey, and was recently published in the journal Current Biology.
Because sleep is a period of heightened vulnerability for all animals, cats tend to sleep between 12 and 16 hours a day in elevated locations where threats from below are less likely. Curious about whether felines display a preference for sleeping on one side over the other, Dr. Sevim Isparta of the Animal Physiology and Behaviour Research Unit in Bari and Professor Onur Güntürkün of the Biopsychology group at Bochum launched the investigation.
“Asymmetries in behavior can have advantages because both hemispheres of the brain specialize in different tasks,” explains Güntürkün.
Perceiving dangers with the left visual field brings advantages
The researchers examined 408 publicly available YouTube videos that showed a single cat lying on one side with its full body visible for a minimum of ten seconds. To maintain accuracy, they only included unaltered footage, excluding any content that had been edited or mirrored. Their analysis revealed that approximately two-thirds of the cats were sleeping on their left side.
The explanation: Cats that sleep on their left side perceive their surroundings upon awakening with their left visual field, which is processed in the right hemisphere of the brain. This hemisphere is specialized in spatial awareness, the processing of threats, and the coordination of rapid escape movements. If a cat sleeps on its left shoulder and wakes up, visual information about predators or prey goes directly to the right hemisphere of the brain, which is best in processing them.
“Sleeping on the left side can therefore be a survival strategy,” the researchers conclude.
Reference: “Lateralized sleeping positions in domestic cats” by Sevim Isparta, Sebastian Ocklenburg, Marcello Siniscalchi, Charlotte Goursot, Catherine L. Ryan, Tracy A. Doucette, Patrick R. Reinhardt, Reghan Gosse, Özge Şebnem Çıldır, Serenella d’Ingeo, Nadja Freund, Onur Güntürkün and Yasemin Salgirli Demirbas, 23 June 2025, Current Biology.
DOI: 10.1016/j.cub.2025.04.043
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22 Comments
Headline: “Scientists Reveal Why Cats Always Sleep on Their Left Side”
Article text: “Their analysis revealed that approximately two-thirds of the cats were sleeping on their left side.”
Note the difference, writers. (I know that you want to have catchy headline text, but saying “usually” or “mostly” instead of the misleading “always” would still be effective.)
Even the two-thirds claim is questionable. I did a basic Google, Images search over
sleeping cats
with no other parameters. I found no predominance either way. Cats snoozing on the left side, right side just about as often (or left and right curls), and not uncommonly on their backs, which latter seems a terrible prophylaxis against threats.
Did you or the researchers know that cats have a dominate paw? Tomcats are virtually all left-pawed and pussycats are virtually all right-pawed. How this escaped human notice for all these millennia seems inexplicable, but cats don’t usually write or handle tools. Still they have a dominant paw — as recently shown in tests where a piece of tuna fish was put into a glass tube deep enough so that the cat would use their dominant paw to try to get it (or so says the theory). Only a tiny percentage of cats of each sex seemed to show no paw-preference.
Hmmm…
This gives one pause to think.
Or, perhaps, “paws” to think? 🤔
Which side of the brain are you thinking with? The right one or the only other one that’s left?
Great comment. That shows how just one potential source of bias was ignored by the researchers. What lousy research. This website does a great job of collecting a lot of information on scientific progress. However, sometimes crappy studies get mentioned.
Scientists are spending time studying how cats lay sleeping? Bizarro world
I care. Those who lack curiosity to look for new knowledge seldom find it. Furthermore, sometimes seemingly innocuous findings lead to big breakthroughs. As some people like to say, many discoveries begin with the phrase, “Hmm. That’s funny.”
That does not mean I endorse the study or this article. Considering how easy the research was, this study should have at least mentioned what kinds of bias they tried to detect, such as videographer preference for cats lying in certain positions (unconscious preferences included).
Of our eight cats, at any given time, approximately half sleep in a normal sleeping position, curled left or right side, possibly snuggled into a dog belly or neck. While the other half sleep in a position that can only be described as a contortionist’s nightmare.
As Rome falls, a man from the future will colonize Jupiter.
The description in the article makes no sense. If the animal is sleeping left lateral, left side down, the first eye to see a potential threat is the RIGHT eye, processed by the left hemisphere of the brain.
Exactly!
Brilliant!
Just saw one of my cats laying on it’s right side.
Thank you! I was similarly flummoxed…right eye/left hemisphere first.
*looks down at cat*-sleeping on her right side.
I was about to write the same thing!
As I read this article I look up at our four cats… all asleep and curled anti-clockwise i.e. on their right side! So much for the scientists.
Just saw one of my cats laying on it’s right side.
Having worked with many rescue cats over the years of all ages, this is very anti-scientific.
Cats don’t sleep on just one side.
Often when they feel comfortable they sleep on their backs with their stomach showing. This shows that they’re very content and trust their surroundings.
If my cats are lying against me, they’re lying on whatever side has their back against me, a sign of trust, protection, and family.
Well, the headline is just not right. The article even contradicts the claim of “always”. My cat sleeps on its left or right interchangeably.