Continuity mistake: When everyone is in the dining room at the dinner table, the order of where everyone sits changes between shots. In all moments where it shows everyone sitting, the order is Priscilla, Derek, Jillian, Mort, Muriel, and Carl. But in one shot, the order is Priscilla, Derek, Jillian, Muriel, Mort, Carl.
Continuity mistake: When we first see Joe's police car in his driveway, the lights on top of the car have the blue half on the driver side and the red half on the passenger side, later on in some scenes the red half is on the driver side while the blue half is on the passenger side.
Continuity mistake: When Muriel Goldman dies, everyone gathers up around her. When that happens, you can see Tom Tacker and Meg in the background, although they both disappeared a few scenes earlier. And than when everyone gathers downstairs, they do a body count and discover Tom and Meg are missing and only then are they found.
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. (00:29:30)
Continuity mistake: While everyone is in the secret room Peter finds a blue book on the desk and picks it up to read. Peter's holding this book in his hands when he asks Consuela what happened, and just as Consuela tells him about her nephew, we see another blue book on the desk beside Peter. There should be only one blue book - the one in Peter's hands. (00:20:40)
Continuity mistake: The interior layout of the dining room is visible in many shots, specifically the wall and windows behind the arm chair at the head of the table. After Stephanie is murdered, when Mort shouts to run for their lives, the crowd exits the dining room and they turn right, then everyone runs for the double front doors, opposite the staircase. This means the windows behind the arm chair at the head of the table are at the back of the house, but later when they capture Tom behind that chair, the shot moves backwards through the window and it's now at the front of the house, beside the double front doors. (00:10:50 - 00:37:30)
Continuity mistake: When Muriel disappears after she's been accused, everybody rushes back up the secret passageway stairs to find her, and in the first shot facing the group there's a large green desk pad on the desk, but in the next shot that desk pad has vanished (and it reappears when they split into groups). (00:21:55)
Continuity mistake: When Joe concludes that Stephanie was in the wrong place at the wrong time, the dining room table is still set with plates, wine glasses, etc, but then Joe tells everyone to look around for more clues, and in the next overhead shot as they all exit the dining room the table is bare. (00:15:55)
Continuity mistake: When Lois and Peter pack their suitcases and leave the room, as Lois walks down the hall she stops at Diane's open door. In this first shot from the hall there are double doors and a blank wall opposite Diane's open door, but in the next shot from inside Diane's room there's a painting hanging on the wall opposite her door. (00:39:55)
Continuity mistake: When Peter and Lois are packing their suitcases, in the first shot Lois is removing things from the dresser's wide middle drawer, but as Peter and Lois walk out of their room that wide drawer has been replaced with two small drawers in the middle. (00:39:30)
Continuity mistake: In numerous shots we see the interior layout of the dining room, with the four sets of two story windows behind the arm chair at the head of the table. After Tom is accused of being the murderer, when he's captured in the dining room they're all behind the arm chair as they crack a joke about Adrien Brody. The problem occurs as the shot pulls backwards through the window, which is an average bay window instead of the four sets of two story windows. (00:37:35)
Continuity mistake: When Brian and Stewie arrive in Leonardo's atelier we know that they are in Florence for two reasons: because of history and because we see Palazzo Vecchio (which is in Piazza della Signoria, in Florence) outside the window. Then when Stewie and Bertram are fighting with Leonardo's flying machine the city of Florence is wrongly represented as if it was Venice, with the see, the lagoon and the canals.
Continuity mistake: When the guests walk through the secret passage, the order of the guests change between shots. First, it's Peter, then Chris, then Carl, then Doctor Hartman, then Seamus, then Quagmire, then Lois. But in the shot of the passage, the order is Peter, then Chris, then Carl, then Lois, then Consuela, then Doctor Hartman. Then when they reach the secret room, the order is Peter, then Chris, then Carl, then Lois, then Bonnie, then Quagmire, then Derek, then Jillian. (00:20:00)