Intelligence

When Portia hears that Antonio is in trouble she first tells Bassanio and his friends to go to the court and then later goes with Nerissa and they both dress up as lawyers and even write a fake letter saying that the real lawyer cant come today because he is sick.

When they both go there, Portia uses her clever wit to save Antonio. she says that sure, the words are "a pound of flesh" but she analyzes the bond and quickly finds out that there is blood written so she uses that as a advantage against Shylock and wins the case.

reference:

https://www.gradesaver.com/merchant-of-venice/q-and-a/explain-how-portia-saved-antonios-life-333560

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