Silence - in the verbal sense.
I had a girlfriend, who is probably my soul-mate if such things exist.... anyhow she and i would study together, go walking together and have lunch together.. but we seldom spent much time talking. We simply enjoyed being in each other's company; and sometimes conversation would have been a distraction from our enjoyment of each other. We were so similar in many ways, that I knew what she would be thinking/feeling at most times and she likewise with me.