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.
Factual error: In all the scenes where Peter wrecks Cleveland's house and Cleveland is in the bath, the tub always slides easily out of the house with Cleveland in it and onto the ground. There are no pipes or any kind of plumbing visible on the bathroom floor where the tub should have been connected.
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.