Why Nictis
Many animals have a third eyelid, and use it exactly when it matters. A peregrine falcon diving at over 300 km/h blinks it again and again to clear debris and keep its eyes clear. A woodpecker hammers a tree thousands of times a day, and a millisecond before every strike its third eyelid closes, shielding the eye from flying splinters and the force of the blow. A beaver slides it over its eyes like swimming goggles and keeps seeing underwater. In every case it closes on its own, and it’s translucent, so the eye is protected at the moment of impact, without ever losing sight.
Scientists call it the nictitating membrane, from the Latin verb nictare, to blink.