When reading silently, the reader might perceive a different tone than the one the writer actually wanted to convey. By listening to the characters' voices, the mood of the scene becomes clearer and the whole act can be understood in the correct way. By reading silently, the reader can introduce his own emotions to the text and misinterpret the message.
Answer:
Readers are unable to create their own voices for how the county attorney and Mrs. Hale might sound live.