Back in the 60s... John Lilly had a lab... dedicated to solving the dolphin communication problem... - James Nestor

If you were to take [a billiard ball]... and... imagine just pushing it inside your head, that's about the volume of your nose and all your sinus cavities. ...[T]hey even stretch out above your eyes... [T]hey call it the because it looks exactly like a seashell.

An infant will reflexively breaststroke when placed when placed underwater and comfortably hold his breath... longer than many adults.

[A]fter around 30 feet... the water stops buoying you... and starts dragging you down to the sea floor. ...[T]he deeper ...the more your body changes. ...Your organs allow for the free flow of fluids so they don't collapse. Your brain waves slow down. Your heart rate will slow to about 1/3 its resting rate.