Governing metaphor of the Sentry passage

The governing metaphor in in this passage is the bird metaphor the Sentry uses to describe how Antigone acted when she found Polynices' dead body stripped bare on the ground. The metaphor was, "And she cried out a sharp, piercing cry, like a bird come back to an empty nest, peering into it's bed, and all the babies gone..." (Sophicles, 80) What the sentry is saying is Antigone is like a surprised bird and Polynice's dead body was the eggs that aren't really there anymore. This metaphor reveals about Antigone's character that she really cares about family. To find her brother mangled and bare was a complete nightmare to her when all she did was try to take care of him. This moment is significant into the character development because Antigone's scream leads to her capture and imprisonment.  This moment is significant to the developement of the themes in the play because it forces people in the play to choose loyalty and love over law and reason. For example, the effect of her imprisonment leads Haemon had to choose between his father the king or Antigone his future wife.