At the dinner table when Annie and George are arguing about her engagement, she responds to something he says by saying, "All right, hold on." But if you look closely, you can see she is clearly saying, "All right, hold on a minute." "A minute" has been dubbed out.
In the supermarket, George says that he's removing 4 hot dog buns from the packet of 12 because he only wants 8 buns to go with 8 wieners. Yet he does this with 3 packets of buns. So if he'd just taken 2 packs of 12, he would have the same amount as 3 packs of 8. But then he probably isn't thinking straight because he's stressed with the wedding plans.
When George and Matty Banks are practicing walking down the aisle in their hallway, Matty asks, "Is it right-together-left, or left-together-right?" to which George replies, "Right-together, left-together..." George's last minute reminder, and Matty's "cheat," written on his hand the day of the wedding, "Left-together, right-together," is opposite of what George says in the earlier scene. Oddly, none of the characters do any of the steps and just walk down the aisle normally.
In the opening credits, the wedding invitation from Annie's wedding says that the wedding date is in October. But, when Annie and her parents are discussing the wedding with Franck, they clearly state that the wedding will take place on January 6th.
When Annie and Bryan go to change for their honeymoon, George takes a shortcut. The time it would take for them to change would be significantly longer than the time it takes George to get to the stairs via his "shortcut," though he still manages to miss their exit.
When George is in the jail cell talking to his wife, his chin is resting on the cell bars, but only in the shots when he is facing into camera. In the reverse shots (over his shoulder) he is clearly several inches away from the bars.
After Annie gets home from Rome and her family is at the dinner table, the shots alternate between Annie holding her fork picking at her food when the camera is on her to her arms folded when the camera is behind her.
When the wedding party starts the procession down the aisle at the church, Howard (Franck's assistant) starts out having Nina and Matty proceed on their left feet. By the time the bridesmaids are proceeding down the aisle, Howard's timing is off with the foot they should be on (in other words, if you think "left-right-left-right" in time with the music, they're on the "wrong" foot, even though they're still in step with each other).
When George pulls up outside his house to welcome Annie home, he clearly states that Annie was in grammar school when they bought the house. However the night before the wedding when they are outside playing basketball, she says that she's lived in the house since she was five.
Despite all the practicing and "crib notes" on 'left-together, right-together' it's pretty clear that everyone is walking down the aisle in standard left-right, left right instead of bringing the feet together after each step then continuing with the opposite foot.
Howard calls George Banks at his shoe factory to tell him the wedding is going to cost $250 a head. It is not until much later in the movie, however, George tries to get the cheapest food for the dinner. Obviously the "per head" estimate could not have been made until the menu had been decided.
When Franck is showing the book of cakes to the Banks the price of the cake is $1200, when in reality wedding cakes are sold by the slice. Therefore, the price of the cake wouldn't be a factor until the final guest count, which at that point they didn't know.
When the Cops arrive to complain about the street being blocked with cars, the Police car is clearly seen in front of the house. If the street was completely blocked with the guest's cars, how did it get there?