When Rostov met Sonya in the drawing room, he reddened.

He did not know how to behave with her.

The evening before, in the first happy moment of meeting, they had kissed each other, but today they felt it could not be done; he felt that everybody, including his mother and sisters, was looking inquiringly at him and watching to see how he would behave with her.

He kissed her hand and addressed her not as thou but as you--Sonya.