When we see other people, the sight has never that precise structure about which we learn theoretically: the eyes, the process of seeing, and the objects of our sight.
When the object of sight can also see, the meeting of those two pairs of eyes means a natural aggregation of two similar things. It is a kind of natural aggregation as that which occurs between the cells of the body. The instantaneous act of seeing is part of this naturalness, while its representation as a process betrays the human theoretical intervention into it. The same intervention reveals itself when we divide the aggregation by calling the two persons objects of sight.
Surely, we do not live naturally, but socially, so that we refrain from combining into a whole with the persons we see. The social habits teach everyone to keep some distance from other people.
However, when the human way of aggregation through sexual contact is stirred by seeing other persons in erotic appearances, the natural aggregation of the two pair of seeing eyes revives. Sometimes, the viewers imbued with erotic feelings can hardly be persuaded that the other persons they see are not really so close to them as their eyes tell them.