上集，海倫‧卓斯基博士帶觀眾探索聲音如何產生；今集，她會發掘我們聽到聲音的原理和用處。原來，早期陸上生物為了聽到聲音，身體曾經過神奇的演化。我們的聽覺也運用了簡單而有效的物理原則。有了聲音，動物可以捕捉獵物，又可避過危險。人類也學懂利用聲音來探索海底的歷史遺跡，甚至是遙遠的外太陽系天體。

電視版本：雙語廣播（粵語／英語）

In the last episode, Dr Helen Czerski explored how sounds were created. This time, she discovers how we hear and use sounds. She finds out that early land based creatures went through nearly magical evolution to hear sounds, and that our hearing ability employs simple but effective physical principles. With sounds, animals can locate their prey and detect danger. Mankind has also come to learn usng sounds to explore historical sites underwater and even distant planets in the outer solar system.

TV Version: Bilingual Broadcast (Cantonese/English)