Continuity mistake: The amount of mud on number 1's face changes to nearly nothing to loads.
Continuity mistake: When Stephanie runs to the shelf to pick the second volume of the encyclopedia the amount of cats increases/decreases randomly between shots. Also, the amount of books and their position changes.
Continuity mistake: Crosby's tie was open after the jacket was on, then crossed as he says "but just one dance"
Continuity mistake: Number 5 goes to the kitchen and the position of the skunk and the stuff on the counter changes between shots.
Continuity mistake: When Stephanie shows her ants and rabbits to Number 5, the amount of cats on the shelf behind suddenly increases between shots.
Continuity mistake: Ben brings a jacket to Newton, who looks at him. A shot later he is looking at the opposite way.
Continuity mistake: At the beginning of the movie when the "Red Army" approaches, the tank has his barrel locked in a transportation brace. As soon as the tank fires back, the brace is gone.
Continuity mistake: In the scene right after Number 5 almost drives the snack wagon into the lake and the Nova guys are shooting him, you clearly see him get shot in the hydraulic pistons which control his head motions. Yet, in the next scene (in the truck) Number 5 comfortably moves his head.
Answer: There were always 5. You see the 5 during the demonstration. Then, before the lightning hits, we see 4 of them in line, but number 5 was still attached to the generator and not in line. When they go inside, there's a weird cut that makes it look like only 3 made the turn, but if you watch closely you can see there's 4 followed by number 5.
Bishop73