What metaphor does bradbury use to describe the earbuds in mildreds ears? What should alarm the reader about this description

Bradbury describes Mildred's earbuds as seashells. He uses this metaphor in a reference as people hold a seashell up to one's ear to hear the sound of the ocean.

This should alarm the reader because the seashells are used by Montag's society to control information and control potential rebellions. This is a way to control individuals and paint a different reality. Also with the seashells always plugged in people don't have the time or a silence to listen to their own thoughts.