Question

read the passage. highlight the phrase that illustrates what infrasounds are. elephants communicate through sound elephants are very social animals, and scientists have long understood that they communicate with each other through smell and touch. however, there may be another way that elephants communicate: through sound. although scientists have studied various elephant sounds, they now believe elephants make very low frequency sounds that are too low for human ears to pick up. these sounds were first discovered when researchers noticed throbbing sensations in the air whenever elephants were together. special equipment revealed that they were making very low - pitched sounds. these sounds, known as “infrasounds,” can travel several miles. it is thought they are a kind of language that elephants use with each other. the sounds are likely produced over long distances to communicate with other members of a herd.

Explanation:

The passage describes infrasounds as very low - frequency sounds that are too low for human ears to pick up. This phrase directly defines what infrasounds are in the context of elephant communication.

Answer:

very low frequency sounds that are too low for human ears to pick up