Continuity mistake: When the family is eating dinner and George sees kid Annie in pigtails, the plate of food in front of her is very full and in a different order on the plate than when it switches to adult Annie. (00:10:47)
Continuity mistake: When the Bank's first arrive at the MacKenzie's to meet them, they have 3 dogs. For the rest of the movie, and the sequel, they only have 2. (00:28:40 - 00:29:10)
Continuity mistake: During the wedding reception, George (Steve Martin) is called outside to meet with the police because there are too many cars parked in the street. Notice that the police car is curbside completely surrounded by cars. In fact, the whole street is packed with cars, making one wonder how the police car got up to the house.
Continuity mistake: When Annie and her family are in the living room while Franc and his assistant are designing the reception, her hair is down. A couple shots later, her hair is tied up and she is wearing different clothes.
Continuity mistake: When Annie visits Franc's shop for the first time with her parents, they are sitting on the couch in front of the window and you see a man in a tan suit walk past, then the frame switches and then switches back to them and that same man walks past again.
Continuity mistake: During their first visit to meet Franc George, Nina and Annie are sitting on the couch. When they are first discussing the date of the wedding and the camera is focused on them you hear Franc close his appt. book, but when the camera goes back to Franc you hear the same sound as he closes the book again.
Continuity mistake: From the outside, the Banks' house has two living room windows. On the inside there are three windows.
Continuity mistake: When the bride-to-be, Annie, runs in the front door upset, George and Nina, her parents, are standing in the dining room looking through all of the tacky presents Annie and Brian have received. George is holding a silver tea set on a platter. In every shot that flashes back and forth between he and Annie, the teapot seems to turn itself in a different direction on the platter.
Continuity mistake: When Nina is sitting at the table during brunch with the in-laws (and George is running around the pool outside) in the wide shots her hands are up under her chin, and in the closeups they're flat on the table.
Continuity mistake: During the scene where Franc and the other consultants are planning the wedding in the Banks' living room, Steve Martin tries to show the construction worker how to open the French doors. The jacket of his (old) tux splits as he is struggling with the door. If you watch the scene is slo-mo, the back seam of the jacket splits as Steve Martin is bending down to reach the door knob, the seam "reconnects", and then splits again, the second time with the ripping fabric sound effect.
Character mistake: A big deal is made about how to walk down the aisle. At home, George shows Matty it's left-together-right. Then at the church, Matty has it written on his hand, but it's right-together-left. Then Frank's assistant mentions it as right-left. But then as everybody is walking, they're strolling casually down the aisle as if in a park, with no regard to the whole issue.