Some animals have an incredible ability to sleep with their eyes open due to unihemispheric slow-wave sleep (USWS); where one half of the brain can rest while the other half remains alert to watch out for predators. Here are five animals who sleep in this unique way:
Dolphins are social and intelligent aquatic mammals that can sleep with one eye open, to stay alert in case of an attack by a predator.
Owls are nocturnal birds who stay awake during the night and sleep during the day. They often sleep with their eyes open to not only watch out for any threats but also look for prey.
Some penguins who live in an environment with constant threats and need to stay vigilant do so by keeping their eyes partially open when they sleep.
Instead of eyelids, snakes have a thin, transparent membrane that protects their eyes from dust, sand, and other particles. Therefore, they can’t close their eyes even while sleeping.
Some rabbits can also sleep with their eyes open. This helps them to be alert and watch out for predators even when they are sleeping. Sometimes pet rabbits also sleep with their open eyes.