Colleen Farmer used it to study how an iguana breathes.

She threaded an endoscope—a tube with a light and a camera at the end—into the lizard’s nose, while allowing it to inhale the artificial smoke from a fog machine. The smoke, though harmless, contained small particles, and the camera could detect these they worked their way into the iguana’s lungs.

And to Farmer’s surprise, no matter whether the lizard breathed in or out, the smoke particles only moved in one direction.