Antonio, holding the horoscope, runs into Bosola in the middle of the night.
He covers for himself by saying that the paper he's holding is actually an astrological "setting" for the Duchess's supposedly stolen jewels. And, hey, what's Bosola doing here anyway?
Bosola says he's just going to say his prayers, but Antonio thinks something's up. He's definitely suspicious of the guy.
Antonio tells Bosola he suspects he poisoned the Duchess with the apricots. Damn it, he knew those apricots looked shady, man. In fact, he says he thinks Bosola stole the jewels, even though Antonio of course knows that the robbery never even happened.
Things get heated, and after exchanging insults for a bit Antonio gets a nose bleed. He's really worked up, apparently. Nose-bleed levels of upset right there.
He whips out his handkerchief, but in the process accidentally drops the horoscope onto the floor.
Antonio doesn't notice, and leaves it there for Bosola to pick up once he's gone. Oops.
Apparently Renaissance-era horoscopes are a little different from the you'll-meet-somebody-tall-and-handsome-this-month ones you see today. This is as good as a birth certificate proclaiming the existence of the Duchess's newborn son.
Almost as good, that is. Bosola now knows the Duchess has just had a son and figures that's why Antonio's having all the courtiers locked up, but he doesn't yet know that Antonio's the father, only that he's covering for the Duchess.
Bosola makes plans to have Castruchio bring the news to the Cardinal and Ferdinand in Rome, knowing it's going to piss them off beyond measure.