Continuity mistake: After the first dinner scene with the family, Dale finally decides to leave and head upstairs. He places his napkin down next to his plate. In the next shot it has vanished. It then reappears a few shots later. (00:10:15)
Other mistake: In the scaring simulation room, the alphabet wallpaper border at the top of the wall has the "J" written backwards.
Suggested correction: The walls of the room also have nonsensical drawings like a giraffe with two heads. The implication is that the monsters designing the room didn't entirely know what kids would actually have in rooms (like they didn't know that giraffes don't actually have two heads). So they thought that humans have the J backwards.
Whether or not the backwards J was intentional or as a joke, it would still seem unreasonable for the monsters to get it wrong when you see they got the pictures for each letter seen correct "jaguar", "kangaroo "pig", "quail", "rhino." I would at the very least call it a character mistake.
As the original correction said, it's just an example of the monsters not understanding the human world. Not a mistake.
Yet they know the alphabet? I doubt it.
Continuity mistake: After Evangeline has left with Aunt Adelaide, Nanny McPhee enters the children's room, and as she and Chrissie walk to the bed they pass Eric's, Lily's and Tora's beds, with the bare wood floor at the center - there is no rug. However, when Nanny McPhee leaves their room the long red and white rug is at the center of the floor, between all the beds. (00:51:55 - 00:52:55)
Continuity mistake: When Matilda makes the chalk write the message on the blackboard, the writing changes. Watch the "Agatha," especially. The handwriting changes and the comma changes length, as well as most of the message changing. Also at the end of the message Matilda "writes" two long lines under it, which cross over. Yet later when Miss Trunchbull flies off the globe you can see there is just one line under the message, not two. (01:20:20 - 01:23:00)
Revealing mistake: During the honeymoon sequence at the end of the film, if you look at the right top of the flowers in the vase during the "flowers covering nipples" bit, you can see a bit of red duct tape covering Liz Hurley's nipple from behind the flowers. (01:22:20)
Revealing mistake: In the dance sequence, we see Elaine twirling Ted around and throwing him into the crowd. Watch the top-right-corner of your screen, as the stunt-double lands in the audience you can see Robert Hays (Ted Striker) in the top-right-corner waiting to pop out. (00:19:10)
Continuity mistake: When Mrs. Waterhouse walks into the livingroom and greets her three babies, there is a large area rug in front of the coffee table. However, as the babies fly towards her in the wide shot facing her, that area rug is gone! (00:22:55 - 00:23:50)
Visible crew/equipment: At the beginning of the movie when Clark is entering his house and the camera angle is from inside, just as he opens the door there is something red on his front porch. If you look at any of the previous scenes, that red thing isn't there. It's the bottom of a sunscreen being used to block the bright sunlight (which would have flooded the camera) behind Clark as he enters the house. (00:01:44)
Continuity mistake: When drunken Stewie is talking at the breakfast table to Brian, Brian has bacon and only one egg on his plate. After Stewie leaps from the shelf, Brian suddenly has two eggs.
Revealing mistake: When Jackie rescues the kid from the burning petrol truck you can see that they used a dummy when he dropped the kid. (01:11:36)
Visible crew/equipment: When a gremlin attacks the Mum from a Christmas tree, and the tree falls on top of her, you can clearly see a member of the crew with eyeglasses, wearing a red shirt, standing behind the tree pushing it forward on top of her. (00:54:30)
Continuity mistake: In the flood scene when Natalie walks in and begins to scream, Kevin is standing on the first step of the stairs with his shirt uneven, and the strings for his pants are showing. In the next shot, Kevins clothes are neatly ironed, his shirt is even, and the strings have disappeared. (00:28:30)
Continuity mistake: In the scene in the library, when Evie is putting back the books. She leans over to put the book back, but it falls to the ground and she is balancing on the ladder. When the camera cuts back to show the whole ladder, the book is nowhere to be found on the floor. (00:13:00)
Continuity mistake: When Nino goes to 'Les deux Moulins' for the first time, we can see Amelie writing the menu on a glass right behind him. A few shots later, we see the glass again and the handwriting is quite different. That's easy to see if you look carefully at the 'd'. Later on, we see the glass once more, and the handwriting has changed again. (01:32:55)
Continuity mistake: When Memphis is driving Eleanor he backs up and hits the right rear-view mirror. He stops, leans out the window and sees that it is dangling. The very next shot it is back to normal and it stays that way for most of the rest of the movie. (01:34:34)
Continuity mistake: When Russell Crowe first pulls in front of Hank Azaria his car's quite angled on the road as he gets out. When we see a wide shot after they finish talking, the car's now much straighter without anyone having gone near it.
Continuity mistake: Mr. Svenning's junior college class ring mysteriously jumps from his left hand to his right hand just in time to get stink-palmed by Brodie.
Continuity mistake: During the scene where Brodie talks to Jay and Silent Bob about Bluntman and Cronic, he shows them a copy of Wizard magazine with a related article. On the right page is a picture of Holden and Banky. They then take this magazine and eventually show Holden McNeil the same article. The right hand pictures are different from how they were before.
Continuity mistake: During the General Patton speech before the football game, "Gill Harris" approaches a player wearing the number 19 on his jersey, who is black. During the football game you notice the player wearing number 19 on his jersey is now white. (00:45:45 - 00:47:00)
Factual error: When Chicken Little is in his bedroom, after he scored during his baseball game, he looks into the spoon he is using as a microphone to see his reflection. He looks into the side that is curved away from you. When you look at that side of a spoon your reflection is upsidedown, but Chicken Little's was right side up.