Everything we smell comes from something that released these molecules, which means each molecule is actually a tiny piece of whatever matter it came from. Spooky, when I think of what I might have been inhaling at the pier. But I digress. Almost all creatures outside of the plant world have an ability to sense these molecules. Even if they lack a nose.
Insects have chemical receptors on their antennae, legs or feet.
Salmon and trout locate their original spawning areas by smell. For many animals, smell is even a primary means of communication. The collective structure that allows us to sense and process odors is called the olfactory system. Behind our noses, at the top of the nasal passage, a thousand or so sensory nerve cells called neurons are open to the air we breathe. When binding occurs, neurons send electrical signals to the olfactory bulb, located just above them, in the lower brain.