Why cats prefer sleeping on their left side
The pets sleep for up to 16 hours a day and often curl up or stretch out for a snooze in opportune places.
But the way the animal settles down is not random, and there is an evolutionarily hard-wired logic underpinning it, according to a study from the Ruhr University Bochum in Germany.
Scientists found cats lie on their left side around two-thirds of the time, which shows that it was done deliberately.
They looked at clips on YouTube of more than 400 sleeping cats and logged which side they were sleeping on.
Data revealed that 266 of the cats (66.5 per cent) were on their left side, leaving scientists to conclude this was a survival trait from their history in the wild.
Sleeping on their left side means when they wake, their left eye is able to see the local area unobstructed by the cat's own body. This visual information is then processed by the right side of the brain.
This hemisphere is what processes threats and is responsible for escaping danger as well as knowing an individual animal's position.
This puts the cat at an advantage compared to if it was to sleep on its right side – when the information is processed by the left side of the brain, which is less specialised to aid a swift escape.
Anti-predator vigilance
This leftward preference is just one of the many ways in which cats protect themselves.
'Sleep is one of the most vulnerable states for an animal, as anti-predator vigilance is drastically reduced, especially in deep sleeping phases,' according to the study.
'Domestic cats are both predators and prey (e.g. for coyotes) and sleep an average of 12–16 hours a day.
'Therefore, they spend almost 60-65% of their lifetime in a highly vulnerable state. To reduce predation risks, cats prefer to rest in elevated positions so that predators are more visible to them and the cats, in turn, are more visually concealed from predators.
'In such a spot, predators can access cats only from below. Thus, their preference for resting in an elevated position can provide comfort, safety, and a clear vantage point for monitoring their environments.
'We hypothesised that a lateralised sleeping position further increases the chances of quickly detecting predators (or to identify careless prey) when awoken.'
Threat-processing leftward bias
Pregnant cows are known to prefer their left side while sleeping for a similar reason, experts believe. The scientists also found that the pawedness of a cat, whether it preferred its left or right side, is likely not to blame for the sleeping preference.
A 2017 study found that male cats tend to prefer their left paws and females are more right-paw dominant.
'We are inclined to believe that the significant leftward bias in sleeping position in cats may have been evolutionarily driven by hemispheric asymmetries of threat processing,' the scientists add in their paper, published in the journal Current Biology.
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