How does Cosimo set up the protest against tithes?

He spreads word walking along the vines from vintner to vintner that this is the year the nobles will collect nothing from them, and instructs them how to ensure this. When the day comes and the bailiff asks for the tithe everyone knows he is there to collect but no one offers up, the sound of conch shells being blown arises from every direction with the chanting "Ca ira!" When he threatens violence against whoever sings, guns sound, shooting into the air from the surrounding hilltops and the bailiffs retreat without having collected a thing.