Seals: Breathe Out vs Breathe In

Unlike humans, harbor seals breathe out before diving, instead of breathing in.

Picture from Alaska Department of Fish and Game

They use oxygen already in their blood and muscles while under water, and their heartbeat slows from about 100 beats per minute to ten.  In one breath a seal can exchange 90% of the air in its lungs. Humans can only change 20% of our air per breath.