Continuity mistake: Perdy has a blue collar and Pongo has a red collar. When Roger and Anita fall into the pond, Pongo is pulled in with them, Perdy does not fall in, she is holding on to Anita's torn dress. In the later scene Perdy gets out of the pond and shakes herself off, Pongo is standing there as if he never fell in.
Continuity mistake: In the old De Vil mansion, Jasper is drinking a bottle of wine. He pours it down his throat, then slugs it, then pours it again. When he puts the bottle down, it has hardly lost any wine in it. In the following shot of the wine bottle, the level has dropped even more.