Continuity mistake: When Sam is in his bedroom, after he finds the Cube sliver it falls and dramatically burns a hole through the floor into the kitchen. But Sam's bedroom is over the living room (there is nothing on the ground floor below Sam's elevated bathroom, and in the first movie Jazz hides in this open space), and the kitchen is actually located between the den and dining room, at the other end of the house. If they were to follow the actual floor plan of the house, the Cube sliver would have landed in the area of the piano in the living room, but where would the fun have been in that?
Continuity mistake: While Mikaela and Sam are on the phone with each other (after the failed webchat date the night before), when Wheelie starts reaching up for the safe's combination lock in the first shot, there are no mouse traps on the floor near the short stool to his left, nor are there any cigar boxes. However, in the next shot two mouse traps (a snap trap with cheese bait and a glue trap) and two cigar boxes have all suddenly appeared. Wheelie proceeds to step on the two traps and then stands on the two boxes to reach the combination lock.
Continuity mistake: The Saturn that Mikaela is driving has a moonroof that encompasses most of the roof, over the front and back seats. When the Decepticon Grindor captures them, in the interior shot looking up at Leo as Grindor seizes the Saturn, the car has a solid roof over Leo, which is also seen in the interior shot as they fall.
Visible crew/equipment: When Ron and Sam are discussing college and girls, in the shot facing Mikaela, as she's airbrushing the design on the motorcycle, the reflection of a crewmember (wearing a blue shirt) holding a reflector screen is visible on the chrome surface at the left, and as the camera pans in closer to her its moving shadow is also visible.
Continuity mistake: At the Smithsonian Air and Space Museum, when Mikaela, Sam and Simmons follow Wheelie they reach Jetfire's enclosure with the large information plaque attached to the metal front bar, as Wheelie faces them. Next shot, that whole front horizontal bar is gone along with the information plaque, and Wheelie now faces Jetfire. Then when the Cube shard attaches itself to Jetfire the metal horizontal bar reappears, though the large plaque is still gone, and that bar vanishes once again in the shot from under Jetfire.
Continuity mistake: When Mikaela, Sam and Leo get into the Saturn there are no headrests on Sam's and Mikaela's seats, but when they kill the Pretender and are driving away, the headrests are suddenly there.
Continuity mistake: At NEST headquarters in Diego Garcia, when Galloway arrives holding up the Presidential order document, in the shot from behind him as he walks through the front gate, the booth is to his right (viewer's right) and the vehicle to his left (viewer's left), but in the shot facing him the booth is to his left (viewer's right) and the vehicle is to his right (viewer's left).
Continuity mistake: In Sam's dorm room, there is a white mini fridge at the foot of his bed, flat against the wall under the Cloverfield poster. However, when Sam rushes after Mikaela just as Alice's 'tongue' grabs hold of his neck, that fridge has moved to in front of the closet door, but it moves back to its original position thereafter.
Continuity mistake: During the forest scene where Optimus Prime is engaged in a battle to the death, Sam is scrambling for safety. In some of the shots both of his hands are uninjured, but in other shots you can see that his left hand is bandaged/splinted. (This is a result of his "real life" injury in a car accident during filming.)
Continuity mistake: When Judy goes upstairs to pack after finding the baby booties, behind Ron there is a chair at the head of the dining room table, in front of the box he just taped. Then, just before Ron says, "Your mother and I are really proud of you," that chair has vanished, only to reappear when Judy shouts that she's crying again.
Continuity mistake: When the Cube sliver burns through the floor and falls onto the kitchen table, in the overhead shot there is a red stool on the side of the table (bottom of screen) with the bowl of cereal, but as the appliances transform that stool is at the wall beside the doorway. It reappears beside the table a few shots later, as the transformed blender jumps on it.
Continuity mistake: When Sam is on the cell with Mikaela, telling her about the long distance relationship kit, he reaches for the webcam with his right hand outstretched while holding the cell with his left, but in the close-up it's his left hand picking it up, while holding the cell with his right hand.
Continuity mistake: When Sam phones Mikaela after missing their webchat date he drops his books and papers, and one book falls upright on the top stair in front of him, which promptly vanishes and then reappears as the last book he picks up. All the books and papers keep changing in his arms between shots as well.
Continuity mistake: When Alice and Leo walk in on Sam in the symbol filled dorm room, on the wall at the head of Sam's bed are three small-to-medium sized framed photos of Sam and Mikaela hanging vertically. After Alice pushes Leo out of the room, the frames change. Now there are two large and medium frames hanging vertically and another medium frame hanging horizontally.