Have you heard the saying about “sleeping with one eye open”? It’s a bit of metaphoric advice about staying vigilant—and a way to describe very light restless sleep. But sleeping with eyes open is ...

If you’ve ever shared a bed with someone with nocturnal lagophthalmos, especially if they didn’t warn you in advance, it’s ...

Most animals close their eyes when they sleep. But did you know some amazing creatures can actually sleep with their eyes open? It might seem strange, but these animals have developed abilities to ...

Some animals, including dolphins, whales, crocodiles, and ducks, can sleep with one eye open. This unique adaptation, called unihemispheric slow-wave sleep, allows them to rest while staying alert to ...