Other mistake: When Doug is saying that Arthur does nothing that Deacon just listed, there is a camera angle of him walking down the aisle with Deacon. In this camera angle only there is a blip to the top right of the screen. This little black mark stays in shot while the camera is moving and is only in this one angle. In other shots of the same angle the black mark is not present. Clearly something was on the camera lens during filming.
Other mistake: When arguing with Carrie about having some of the festive cheese platter, Arthur goes for a "spoon to the wheel of brie", but from a previous episode (Ticker Treat S4, E6) we found out that Arthur has banned soft cheeses along with celebrating Halloween.