What Does Sentry Mean?

In the passage where Sentry is describing Antigone, the main metaphor is comparing Antigone to a bird. In line 471, Sentry states, "And she cried out a sharp, piercing cry" He also says in line 474, "she bursts into a long, shattering wail". Comparing Antigone to a bird is showing that she could be a free spirit but also act like a mother bird hen it comes to her family. This is very important to her character development, in which you get a sense of foreshadowing