The animal that has unidirectional airflow through its lungs is the bird.

Here's why this is important:

* Efficiency: This system allows birds to extract more oxygen from the air, which is crucial for their high energy needs during flight.

* How it works: Unlike mammals, where air flows in and out of the lungs through the same passage, birds have a system of air sacs and parabronchi that allow air to flow through the lungs in a continuous loop. This means fresh air is constantly passing over the respiratory surface, maximizing oxygen absorption.