Why do 99% of cats sleep on their left side?

A new study has revealed an interesting behavior in cats: the majority of them tend to sleep on their left side.

Scientists believe that this position may be a defensive strategy, helping cats react more quickly to potential threats.

Cats have long been known to sleep in high places, such as on top of suitcases or wardrobes, out of reach of predators on the ground and even affectionate owners.

This behavior helps them easily detect threats from a distance. Researchers theorize that a cat's sleeping position – whether on its left or right side – may also serve a similar defensive function.

"Behavioral asymmetry can be advantageous because both hemispheres of the brain are specialized for different tasks," explains behavioral neuroscientist Onur Güntürkün from Ruhr University Bochum in Germany.

Güntürkün and his team analyzed the sleeping positions of cats using 408 carefully selected YouTube videos. The results showed that the majority of these cats (two-thirds) tended to lie on their left side. This position allows their left vision to be unobstructed by their own body.



The left visual field transmits signals to the right hemisphere, which is involved in spatial awareness, threat recognition, and rapid escape coordination. Therefore, this sleeping position may help cats react faster when awakened by predators (or humans approaching).

“Sleep is one of the most vulnerable states for animals, as their ability to be alert to predators is greatly reduced, especially during deep sleep,” the study authors note.


The researchers suggest that the fact that most cats tend to sleep on their left side may stem from an asymmetry in the brain’s two hemispheres when processing threats. However, they also note that other factors that may influence this behavior cannot be ruled out.