The Third Eyelid

The Nictitating Membrane

From these photographs you could easily imagine that the animal kingdom had suddenly been enveloped in its own zombie apocalypse. Yet these pictures do not feature the Squawking Dead.
Thanks to high speed photography, these pictures capture the nictitating membrane in action. It is also known as the third eyelid, haw and the inner eyelid. It is drawn across the eye to protect and moisturize it while retaining visibility.