Final answer:
Antigone criticizes Ismene's cowardice when Ismene says she'll be silent about Antigone's plan to bury their brother, showcasing Antigone's commitment to her beliefs over fear of punishment.
Step-by-step explanation:
When Ismene tells Antigone she will be silent about Antigone's plan to bury their brother Polyneices, Antigone throws back in Ismene's face her cowardice. Antigone is confronted with a moral dilemma and decides to act according to her beliefs about familial duty and divine law, despite the threat of death. Ismene, on the other hand, expresses her fear and unwillingness to defy Creon, the king, thus prompting Antigone's criticism of her sister's lack of courage.