When police put up a warning sign for Bluebeard in Paris, the writing is in English. It should be in French.
When the artist is going to paint the model "unobserved", it's done so by arranging mirrors so he can see her but she supposedly can't see him. In reality, however, no matter how many mirrors you use or how you arrange them, if you can see another person in the reflection(s), they can see you.
A cravat with which Bluebeard supposedly strangles his victims features prominently in the plot, but every time we actually see Bluebeard strangle someone, he does so with his bare hands.