Birds and aquatic mammals are capable of unihemispheric slow-wave sleep (USWS), which means they can sleep with one eye open and one hemisphere of the brain awake. USWS helps dozing aquatic mammals such as dolphins keep breathing, presumably by permitting them to surface once in a while. It also lets sleeping birds keep an eye out for predators--literally. This was demonstrated in an experiment reported in Nature earlier this year. Neils C. Rattenborg, a graduate student in the department of life sciences at Indiana State University, lined up four groups of four mallards. (Yes, he got his ducks in a row.) Then he videotaped the birds while they slept. He found that those on the ends of the rows--those more exposed to predators--had two and a half times as much USWS as the birds in the middle of the group. A bird on the end kept its outer eye (the one facing away from the group) open 86 percent of the time, whereas birds in the middle kept it open only 53 percent of the time. Brain-wave tests confirmed that half the brain slept and half was in a "quiet waking state," alert enough for the duck to escape should danger threaten.

Thanks, Cecil!

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The more you know!

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*quality

Boosting this quality contribution up in the Hot Listing - declared quality by GenjiKilpatrick.

I think the real moral of the story is your puny human eyelids will not protect you from ARROWS.

But on the plus side, after the arrow hits, you won't blink any more. You won't be able to.

Pretty sure humans do in fact have a vestigial third eyelid. That little red blob of semi-transparent shit in the corner of your eye? Yup, there it is.

Anyway, turns out the blind blink isn't antiquated at all. Theres probably a good reason why we got rid of it too, I mean, thats how Evolution works.