I thought the third eyelid was simply a fun party trick cats pull out when they get together. It turns out that it actually has practical properties. Back in the day, it was regarded as a vestigial organ, like an appendix, but we know better now.
Many animals have the nictitating membrane (aka third eyelid), and the fact that humans and primates do not is curious. I think it’d be handy for cutting onions, anyhow!
Why Do You Have to Close Your Eyes Like That?
By Sarah Donner
When the night has come and you curl up on your bed
Kitty comes to you and lays down her fuzzy head
When she’s getting sleepy, that’s when it arrives
A hidden mucous membrane, the creepy third eyelid
Why do you have to close your eyes like that
You creepy little cat?
It’s a fold of tissue, a measure of protection
Holds the tear film to the cornea better
It’s a little windshield that guards from the debris
When you’re hunting prey through the tall grass and the weeds
The sympathetic nervous system regulates the lid
It’s translucent tissue, so they don’t see much through it
Why do you have to close your eyes like that
You creepy little cat?
You remind me of a zombie or the chick from X-Men
Or the evil witch in Robin Hood, the one with Alan Rickman
Why do you have to close your eyes like that
You creepy little cat?
SOURCES: Catcentric, Scientific American, Wikipedia
