Jen is trying to put together an audio database of animal sounds for Mr Hammond's birthday, but one sound, resembling a howl, eludes them. Andy jets off in his safari-mobile to the Sonoran desert in America in search of the mystery sound and the animal that made it. Along the way, he meets a grasshopper mouse and escapes a pack of hungry harris hawks.

When clouds of sand block the underwater cameras back at Safari World, Jen is unable to show Mr Hammond the footage of their male pufferfish building its nest. To the rescue comes Andy, who jets off in his safari-mobile to the coral reefs of Japan to find another male pufferfish building a nest so he can re-record the action on his gizmo.