Plot hole: In this episode Arthur scams Deacon and several other parents for phony piano lessons because he doesn't actually know how to play the piano. However, earlier in the series (Art House episode, S1 - E24) we learn that Arthur can play the piano when he temporarily moves out and after his house warming party Doug says to Carrie, "Who knew Arthur could play the piano like that?"
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Revealing mistake: When Doug and Deacon are driving round trying to find Gabe's Pizzeria, they get into the car and pull out into the road. However if you look at the traffic, they would have hit at least 2 cars in doing so. But they don't, showing it's a projection.
Continuity mistake: Carrie tells the preacher that she and Doug met at a bar. When she hears the lie about her falling on Doug as a kid, she believes it and acts as if that was their only meeting before the bar. But in the episode "Road Rayge", she mentioned a junior high school dance where Doug asked her to dance.
Continuity mistake: In this episode, Doug looks out his bedroom window and sees his parents and Arthur standing on the porch by the front door, but in season one, the episode when Richie sleeps with their neighbor, Carrie and Doug's bedroom window faces the Sacksi bedroom window.
Visible crew/equipment: When Arthur comes out the basement singing Silent Night, he stops and waits a few seconds while trying to remember the next line. Carrie prompts him for this and he thanks her and walks off. As he does, the camera changes angle and a tape marker can be seen on the floor where he stopped to remember the next line in the carol.
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.
Visible crew/equipment: Throughout this episode you can see stage lights reflecting off Carrie's glasses most notably in the bedroom when Doug finally convinces her to join the party. She looks toward the camera and a series of stage lights are reflected very evidently.
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.