The "telegrams" that are essential to the plot are written on blank pieces of paper instead of the telegraph company's letterhead, which would have been the case with actual telegrams.
Paolo whistles the aria La Donna è Mobile but closed captioning it's erroneously called La Donne Nobile.
Neapolitan and Sicilian dialects are separate and distinct. This should have made the defendant's true city of origin quite evident to all the native Italian speakers.