Imagine a rat scurrying along a busy street in a big city. It's dinnertime, and various smells waft through the air.

Through the mix of smells of cars, people, businesses and (yuck!) garbage, it catches a momentary waft of something delicious — a dropped slice of pizza or a thrown-away tray of lunchmeat. The rat knows that's what it wants to eat. But where is it? How will it use odor to find its way?

Odor is important for many animals. Odors help animals find food, find mates, avoid predators, and defend their territory. Here, we'll explore how animals sense odors that indicate food. We'll also learn how their brain initiates tracking behaviors to find that food.