How do dolphins sleep?
By covering their face with fins.
No.
Like humans, dolphins are mammals.
They breathe through lungs.
Hence, dolphins need to come up to the surface of water at regular intervals to breathe.
Also, dolphins have to protect themselves from dangerous predators.
Hence, they always need to be alert.
Just like security guards, right?
Just listen.
Each eye of a dolphin is directly connected to the opposite hemisphere of the brain.
Now, while sleeping, a dolphin shuts down one hemisphere and the opposite eye.
In the meantime, the other active hemisphere keeps track of internal bodily functions like breathing.
The open eye looks out for predators.
After 2 to 4 hours, the dolphin swaps the sleeping task.
It awakens the closed eye and resting hemisphere, and shuts down the active hemisphere and the open eye.
This type of sleep is called uni hemispheric slow wave sleep.