Amazingly, snakes smell with their tongue. Their tongue is the red and thin wire like ligament that is usually sticking out of their mouth.
As you know, humans take in the air particles through their nostrils, which then goes through the livers and is pumped by the heart to all over the body. Snakes absorb these particles using their tongue. Then these particles are transfered to an organ behind the snake's mouth called the Vomernasal Organ or Jacobson's Organ, where they are examined.
This is one of the reasons that snakes flap and wiggle their horrifying tongues out of their mouths most of the time.
Now let's take a look at a relatively friendly and playful marine: the dolphin, which sleeps with half its brain in the awareness state.
Like all other mammals, dolphins have a brain with two hemispheres (halves). These mammals have the ability to send one to sleep while the other stays in action. Dolphins remain under water for fair time span but still need to resurface. The awake hemisphere takes care of the resurfacing cycle and also keeps guard for any probable threats.
In captivity, the dolphin feels more secure and is sometimes observed to be resting both its hemispheres at once. But how does it breathe in this case? With a reflex tail-flick.