An international research team analyzed hundreds of Youtube videos of sleeping cats. Goals, I know. But what they found may seem somewhat surprising: cats strongly prefer sleeping on one side over the other. Specifically, the left one. Researchers say this may have been helpful for them as they evolved to escape right after waking up.
It might sound like a quirky trivia fact, but this nap-time preference could reveal something deep about how cats — and possibly many other animals — experience the world.
Purrfect adaptation
Out of 408 original, unedited YouTube videos of visibly napping cats, roughly two-thirds were lying on their left side. That’s not a fluke. The statistical analysis showed a clear leftward bias: 266 cats (about 65%) snoozed on their left, while only 142 chose the right.
Why does this matter? Cats take their sleep very seriously (they need 12-16 hours of it per day), and there’s a reason they lie more on the left. According to the researchers, it all comes down to brains — and survival.
Cats that sleep on their left side, can perceive their surroundings upon awakening with their left visual field. This is processed in the right hemisphere of the brain, the authors explained. This hemisphere is more specialized in spatial awareness, the processing of threats and the coordination of rapid escape movements. In other words, it gives cats a slight advantage if, say, a coyote is approaching while you’re napping.
“Upon awakening, a leftward sleeping position would provide a fast left visual field view of objects that approach from below or from similarly elevated positions,” The authors wrote.
Cats already take precautions. They tend to nap in elevated spots — tree branches, bookshelves, kitchen cabinets — where it’s harder for predators to sneak up. “In such a spot, predators can access cats only from below,” the researchers noted. Sleeping on the left side may be a final evolutionary cherry on top of the defensive cake, a subtle tweak that lets them wake and instantly scan the space below or to their left.
“Sleep is one of the most vulnerable states for an animal, as anti-predator vigilance is drastically reduced, especially in deep sleeping phases,” explains Professor Güntürkün and colleagues, quoted by Sci News. “Domestic cats are both predators and prey and sleep an average of 12-16 hours a day.” That’s around 60-65% of their lives spent in a state where being wrong about the surrounding environment could mean being dinner.
Asymmetrical brains
This behavior fits into a broader scientific understanding of asymmetry in animal brains. Many species, including humans, show a preference for using one side of their body or one eye over the other. Most humans are right-handed, and most cats (and dogs) are right-pawed. This lateralization offers important evolutionary perks.
First, by consistently favoring one side of the body — like always reaching with the same paw — the opposite side of the brain gets more training. Over time, this leads to more efficient processing. Think of it like always using the same hand to write: the more you do it, the better and faster you get. Second, by dividing up responsibilities between the two hemispheres, brains can do more things at once. One side can handle language or social cues while the other focuses on spotting danger. This parallel processing avoids redundancy and makes cognition more efficient.
That brings us back to our snoozing cats.
Ancient instinct
By sleeping on their left side, cats keep their left eye and visual field more exposed when they wake up. This setup funnels information straight to the right hemisphere of the brain, giving the cat a faster reaction time if something unexpected enters its field of vision.
One key limitation of the study is that it relied entirely on publicly available YouTube videos, which means the researchers had no control over important variables like the cats’ age, sex, breed, health, or pregnancy status. Pregnant cows, for example, lie more often on the left — but the researchers couldn’t assess whether the cats they studied were pregnant. However, the odds of randomly sampling hundreds of expecting felines are slim.
Ultimately, however, the researchers are confident that most cats sleep on their left side.
So, the next time you catch your cat curled up, left side down and purring, know that it might not just be for comfort. It could be an ancient, brain-based survival instinct kicking in — proof that even in their laziest hours, cats are still a paw ahead.
The study was published in Current Biology.
