Blinking is a normal physiological activity that relaxes the eye muscles. Sometimes when you look into a cat's eyes, you notice they always seem to stare at you with big, unblinking eyes. Many people then assume that cats don't blink at all. But is that really true?
The purpose of blinking is to coat the surface of the eyeball with tears, preventing it from drying out or becoming susceptible to pathogens. The lacrimal glands above the outer corner of the eye constantly secrete tears, which cover the entire eyeball when blinking. The eyelids function similarly to windshield wipers. Except for animals like snakes with transparent eye coverings, all animals with exposed eyeballs should, in principle, blink. So, what about cats' eyes? Animals blink in different ways. Like humans, apes blink with the upper eyelid covering the lower eyelid, while other mammals blink by bringing both eyelids together simultaneously. Furthermore, most birds keep their eyes open when blinking; uniquely, they have a thin membrane (called the nictitating membrane) that quickly opens from the inner corner of the eye to the outer corner during blinking. Incidentally, birds close their eyes by lifting their lower eyelids when sleeping. 
When lions, tigers, leopards, and other felines blink, their upper and lower eyelids usually come together simultaneously. However, nowadays, they often seem not to close completely; the eyelids only move slightly without touching. Closer observation of cats reveals that they do indeed use this method, which is certainly more efficient. Their upper eyelid droops slightly, and their lower eyelid lifts slightly, thus completing the blinking motion. No wonder we often don't notice cats blinking. Although cats' eyes have become larger since becoming domesticated, is it because they can no longer blink effectively? Or do they find blinking too time-consuming? In any case, cats are quite unpredictable. In an experiment, sometimes when you reach out and tap their head, their wide-open eyes slowly close, their reaction incredibly slow. Humans, on the other hand, would close their eyes quickly, while a cat, to make a perfect blink, probably has to move its eyes very slowly.
Cats' eyelid muscles seem less robust, preventing them from performing the rapid blinking motion of seeing a cute girl like humans. However, the question remains: don't cats also have nictitating membranes? As mentioned earlier, birds use the opening and closing of their nictitating membranes instead of blinking; cats also have a similar membrane, often referred to as a third eyelid in birds and cats. If cats couldn't use this membrane to replace blinking, they certainly wouldn't be able to quickly open it. Birds' nictitating membranes can stretch from the inner corner of the eye to the outer corner, covering the entire eye, while cats' nictitating membranes only cover half. A common thread is that both cats and birds close their eyelids and nictitating membranes when sleeping.
Some mammals also use an open nictitating membrane instead of blinking; the meerkat (Civet cat) is an example, blinking in a manner identical to that of birds. Furthermore, the flesh-colored mucous membrane at the corner of the human eye is said to be a remnant of the nictitating membrane. This means we can consider the cat's nictitating membrane as a remnant of a vestigial state. Although cats can no longer blink using their nictitating membrane, it will be visible if their eyes are tightly closed, such as when they are sleeping. Even when applying eye drops, the nictitating membrane will protrude if their eyelids are everted.
Simply put, this might be why cats can't blink their eyelids forcefully. If they blinked forcefully, the nictitating membrane would protrude and cover their eyes, but it couldn't quickly retract, causing problems. Birds' nictitating membranes are semi-transparent, so even if they cover their eyes, it doesn't obstruct their vision. In contrast, cats' nictitating membranes are very thick; if their eyes were separated by this membrane, they couldn't see clearly at all. Perhaps this is why they can only move their eyelids slightly or slowly close their eyes to prevent the nictitating membrane from accidentally protruding again.
So, cats blink just like humans. Blinking is a way for cats to communicate; keeping their eyes open means hostility, while blinking means friendliness. If your cat isn't very affectionate with you, you can't just stare at it; you should blink to show affection.
In terms of blinking frequency, cats' eyes are very resistant to dryness, generally blinking only once every 3 to 4 minutes. Compared to humans blinking an average of 10 times per minute, cats blink almost 30 times more frequently! So if you want to observe a cat blinking, please be patient.
