上集，海伦‧卓斯基博士带观众探索声音如何产生；今集，她会发掘我们听到声音的原理和用处。原来，早期陆上生物为了听到声音，身体曾经过神奇的演化。我们的听觉也运用了简单而有效的物理原则。有了声音，动物可以捕捉猎物，又可避过危险。人类也学懂利用声音来探索海底的历史遗迹，甚至是遥远的外太阳系天体。

电视版本：双语广播（粤语／英语）

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)