Some animals do it for survival, while others have evolved this ability for different reasons. It might seem strange, but these animals have developed abilities to rest while staying alert to their ...

A recent study observed sleeping participants' pupils during sleep, using a new method that could have implications for studying sleep disorders. Reading time 2 minutes Though sleep is a time to power ...

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 ...

Birds resting on a beach or a wire often look calm, almost detached from what is happening around them. But that stillness can be misleading. For many species, sleep is not a full shutdown. One eye ...

CNN — You walk over to your friend who is asleep on your couch, snoring away. You bend over to goose him when suddenly you jump back in shock. His eyes are open ...