Question

When someone talks quietly they___ complete the sentence

Answer 1

answer is :-

whisper

Answer 2

When someone talks quietly, they Whisper.

Whispering is an action of speaking very softly and quietly that only the  person sitting near you can hear.

According to Cambridge English Dictionary,

Whisper is to speak very politely and gently using one's breath and nose instead of throat so that only the near one could hear the speaker.