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.
Continuity mistake: When Derek Wilcox is killed and on the ground, he is on his front with his head turned. He got hit above his right eye and blood is coming from underneath him, but after everyone else arrives outside, he is on his back with the wound above his left eye and blood is all over his face.
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.
Continuity mistake: As Stewie is about to eat his brisket (just before he throws it at Meg) he is cutting part of it off. Just as he cuts through the shot cuts and you can see the brisket is now back in one whole piece. You can also see the mashed potatoes change from white to green.