Which animal sleeps with open eyes?
Snakes actually sleep with their eyes 'open', as they don't have eyelids to close their eyes. Instead, their eyes are covered with transparent scales which protect their eyes and stop them becoming dry – these are called 'spectacles'.
These freaky creatures prefer to sleep with their eyes open. This is down to a cool evolutionary feat called unihemispheric sleeping – the ability to rest one half of the brain at a time, leaving one eye open to look out for potential attacks. Or in some cases, just a lack of eyelids!