Continuity mistake: When the flag team first walks out to the field, they are all in a straight line. Next time they are in two seperate lines with Meg at the head. Also, the girl with the head brace moves to the front when she is seen in the back. There is not enough time for them to move into the lines.
Continuity mistake: In the end of the episode whilst the families are eating lunch at the picnic table there is a lot of plates of food and glasses on the table. Towards the end of the scene Brian says "I guess some mysteries are better left unsolved", there is a wide shot after he says this and every plate and glass from the table has disappeared. (00:21:25)Lummie
Continuity mistake: Just after the guests have found Muriel, there is a shot from outside the manor where we can see Quagmire's car at the back of the rest of the cars. But in the next overview shot of the manor, Quagmire's car is now in front of a red car. (00:29:30)Casual Person