A
shark swings its wide head back and
forth. T is hammerhead is hungry and looking for food. As it hunts, the shark sucks water into its nostrils. T e water carries the smells of seaweed,
sand, and sea creatures. It rushes through tubes inside the shark’s snout and brushes by smell cells. T ese cells pick up scents in the water. T ey help the shark sniff out prey. Suddenly, the shark smells something
it likes. Blood! T e smell comes from a kilometer away. T ere, an injured stingray buries itself in the sand. It’s trying to hide. Yet a few drops of its blood float in the water. For the shark, the smell of blood is a trail.
It leads the shark to the ray’s hiding place. T e shark floats over the sandy spot. T en, in a flash, it pins the ray to the seafloor with its head and sinks its teeth into dinner. A shark can find a hiding ray because the
shark has an amazing sense of smell. In fact, this fish has one of the best senses of smell of any animal. It can smell a single drop of blood mixed into a million drops of water. Many other animals have a super sense of
smell, too. T ese animals rely on it to survive and understand their world. We do, too.
What a Stink! To see how sense of smell works, imagine you’re on a hike. Your dog accidentally startles a skunk. In defense, the skunk sprays a foul fluid. Tiny molecules hold the spray’s odor. T ey float in the air. As you breathe in, these molecules
enter your nose. T ey reach the mucus inside your nostrils. Many get stuck in this wet goo. At this point, you don’t know how bad things are about to get. You can’t smell the skunk stink yet.
4 NATIONAL GEOGRAPHIC EXTREME EXPLORER
Moving On Up Some molecules escape the mucus in your nose. T ey flow into the nasal cavity. T at’s a hollow area behind the nose. Finally, the stinky molecules bump the top of the cavity. T ere, they stick to two patches of mucus. Each spot is the size of a postage stamp. T e molecules are in a sticky spot, but
their trip isn’t over yet. Millions of nerve cells cover these spots. Tiny cilia, or hair-like parts, wiggle at the end of each cell. T ese smell receptors catch the skunk odor. Next, the nerves race information about the
smell to your brain. It compares the new smell to your memories of good and bad smells. Uh-oh. T is one is definitely bad. Suddenly, you smell the stink. It’s worse
than 1,000 rotten lemons. You gag. T en you hold your breath and run. T is whole process only takes about half a second. All of these body parts work together to help you smell. T ey make up your olfactory system.
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