The Nose Knows More Than You Think
A shark's nostrils do not breathe. They are dedicated scent organs, and nothing else. Water flows continuously through two nasal passages lined with sensory cells called olfactory lamellae, folded tissue that dramatically increases the surface area available to detect dissolved chemicals. A large shark can carry more than a hundred of these folds in each nostril. The result is an olfactory system that can register certain compounds at concentrations as low as one part per billion, roughly equivalent to a single drop of blood dispersed through a backyard swimming pool.
