Built to Breathe

A whale's nostrils did not stay on its snout. Over millions of years they migrated to the top of the skull, becoming a blowhole that surfaces with barely a tilt. Unlike fish, whales breathe by choice — every breath is a deliberate act.

That creates a problem: an animal that must decide to breathe can never fully switch off. So whales sleep with one half of the brain awake, enough to keep surfacing while the other half rests. On deep dives their lungs even collapse on purpose, keeping dangerous nitrogen out of the blood.