Voltore enters the street and calls Mosca a fly, saying that his fortune will soon turn for the worse. Mosca tells Voltore not to speak so unsuitably and un-lawyerly, and then exits. Volpone asks Voltore if he should have attacked Mosca, and Voltore recognizes Volpone as the man who has been taunting him. Volpone says he’s furious that a lawyer was able to be tricked by someone like Mosca, who is uneducated, and he expresses his hope that Voltore is just pretending not to be the heir in order to confuse Corvino and Corbaccio. Voltore gets furious and curses out Volpone, and Volpone responds that he knows that Voltore is so wise that he could not possibly have been tricked.
Mosca’s name means fly, which is why Voltore calls him that. Volpone repeats the same joke he made with Corvino and Corbaccio, pretending that he thinks Voltore is acting when really Volpone is the one acting in a disguise. Again, Volpone is indulging his excessive desire to humiliate his suitors. This desire has corrupted his judgement, and it will ultimately lead to his downfall.