How the description of "hertz" in "Animal Sounds" develops an idea introduced in "Incredible Animal Ears.

The description of "hertz" develops the idea of sounds of very low tones and frequencies that elephants can hear, which is explained in "Incredible Animal Ears."

Explanation:

In "Incredible Animal Ears" we are presented with an explanation of how elephants have the incredible ability to hear sounds with extremely low pitch and frequency and promote communication between them, even emitting signs of socialization and danger. This frequency and tone of the sounds are measured by the hertz, which are explained in "Animal Sounds" which shows how the variation of tones is important in animal communication.

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