Silences are something you can talk about
Silences are for you. The therapist is there to talk about what you want to talk about and the silence is time and room for you to let your thoughts come to you. The therapist is also silent as a way of staying out of your way and not distracting you.
Sometimes I say I don't know what to talk about, and viola-something comes to mind.
If you are in a time of silence and it bugs you, that's something to talk about.