When Winston and Julia meet with O'Brien in Book Two, O'Brien tells them that there are things they will need to do in order to show their loyalty to the Brotherhood (the underground revolutionary group who works against Big Brother). He names atrocious acts such as throwing acid in children's faces, murder, and if they are caught, suicide. The one thing they are not willing to do is betray each other. When O'Brien asks if they are willing to do this, Julia abruptly shouts, "NO!" and it could be said that this foreshadows their vulnerability in the future. In this society, love is a threat to both the citizens and the government. It's a threat to the government because it means the citizens aren't entirely devoted to Big Brother, and it's a threat to the citizens because it makes them vulnerable (having something to lose).