I noticed Mary and Vincent didnt wash their hands or use gloves when they were making gnocchi.
I wonder if they wore protection when they made nookie.
We'll never know cause MAry died. If she hadn't maybe there would have been the potential for GODFATHER IV - in which Sonny's Bastard son has a bastard son by incest who takes over the family business, and the Corleones are wiped out because of this infamnia.