Some animals can sleep with their eyes open. This phenomenon is called "semi-sleep."
For example, aquatic animals such as waterbirds and dolphins can choose to keep one eye open while swimming to observe their surroundings, while sleeping with the other eye closed.
In addition, some cats, elephants, horses, cows, etc. can also perform "semi-closed sleep" with their eyes open, so that they can detect potential threats in time and stay alert.
