Arsène was placed in the third cell on the right, and the heavy vehicle started. He carefully calculated when they left the quai de l’Horloge , and when they passed the Palais de Justice . Then, about the centre of the bridge Saint Michel, with his outer foot, that is to say, his right foot, he pressed upon the metal plate that closed his cell. Immediately something clicked, and the metal plate moved. He was able to ascertain that he was located between the two wheels.