Continuity mistake: In the opening attack scene on Soccent AFB, Colonel Sharp pulls an axe off the wall to literally cut the server hard lines. This axe was not on the wall in the earlier dialogue between Colonel Sharp and the one who was telling him about the unidentified aircraft. (00:07:40)
Continuity mistake: In class for his genealogy report, when Sam begins to dump his great-great-grandfather's belongings onto the desk, while the backpack is upside-down it turns around from front to back, between the wideshot and next close-up. (00:08:55)
Continuity mistake: During Sam's family genealogy report, when he holds up Captain Witwicky's glasses to show the class, there are cracks in certain areas of both lenses. Those cracks actually change position and characteristics when we see the glasses elsewhere in the film, such as on eBay and when Prime explains their importance to Sam and Mikaela when they first meet. (00:10:15 - 00:17:40)
Continuity mistake: After class when Sam rushes to his father, who is waiting in his car, and tells him that he got an A-, the license plate is affixed to the front bumper. At the start of the next shot, the front license plate is gone, but it then reappears when they arrive at Bobby B's. (00:11:35)
Continuity mistake: When Ron and Sam, followed by Bumblebee, make the U-turn in front of Bobby B's and then park, the spinning 'Bobby B. sez...let's talk deals' sign is to the left of the three vintage gas pumps, near the clown. When Bobby B. puts his arm around Sam's shoulder and says, "Sam, your first enchilada of freedom..." the spinning sign is now on the other side of the pumps, where there wasn't a spinning sign previously. (00:12:10 - 00:13:15)
Continuity mistake: When Bobby B. walks with Ron and Sam to the main used lot, where Bumblebee and the VW Beetle are located, most of the cars opposite Bumblebee and to its side actually change make, color, etc., from the time Ron makes the U-turn, to when all the windows shatter and shots between. Examples are: there is a camper parked in the fifth space which changes to a car; the yellow hatchback behind Sam when he opens the car door changes to a light blue car; and the two blue cars (one with a spoiler) parked beside Jaime, the ostrich, which change to a dark car and yellow hatchback. (00:12:10 - 00:15:10)
Continuity mistake: When Ron and Sam park in front of Bobby B's, there are three cars parked in front of the three pumps - a white vinyl top, a wagon, and a red car. When Sam says, "You said half a car, not half a piece of crap, Dad," the red car has been replaced with an old blue Plymouth, specifically for the "50-year-old virgin" joke, because the red car is back in following shots. (00:12:20)
Continuity mistake: When Sam is looking at Bumblebee at the car lot, he wipes some of the grease off of the Autobot insignia. When Bumblebee blows out all the windows, all the grease is gone. (00:13:55 - 00:14:50)
Continuity mistake: At Bobbie B's, when Sam first opens Bumblebee's driver-side door, the gas pump's white steel guardrail is directly behind him, aligned with the driver's seat, but when all the windows shatter, Bumblebee's front fender is aligned with the guardrail, though Bumblebee has not moved. Same goes for the VW Beetle beside the Autobot. (00:14:00 - 00:15:10)
Continuity mistake: At the park, when Sam decides to drive Mikaela home, Miles is in the car with his right arm (viewer's left) up behind his head, but in his close-ups his arm is down. (00:22:30)
Continuity mistake: When Bumblebee "breaks down" on the side of the road, a book appears in Sam's hand that wasn't there before. (00:24:10)
Continuity mistake: When Mikaela looks under the hood and fiddles with Bumblebee's distributor cap, her long hair is either behind her shoulders or in front, depending on the angle of the shot. (00:25:15)
Continuity mistake: When Mikaela looks under Bumblebee's hood, in close-up shots, her tummy is shiny and oily. In other shots, it is completely dry. (00:25:25)
Continuity mistake: At the Pentagon, when Maggie is sitting with her team of 'experts' and one suggests Iran, in the shot facing Maggie's back her file folder is closed and lying on the table in front of her, but in the next shot, she closes the open folder. Between these two shots, the analyst to her right goes from holding his headset by his ear, to holding a pen on the book in front of him. (00:27:50)
Continuity mistake: Before Frenzy goes to the POTUS mainframe, aboard Air Force One, in the overhead shot of the cabin the seated Secret Service agent holds in both hands the unopened USA Today, with the back's weather page facing out. Next shot, the newspaper is open in his hands. (00:28:10)
Continuity mistake: Aboard Air Force One, when Frenzy kills the first two Secret Service agents, the second agent falls back into the hallway, but his feet are still in the room over the bottom raised lip of the doorway. When the third agent fires on Frenzy, the legs of that second agent are lying flat on the room's floor, right beside the first agent that was hit. Note that the agent's legs are also beside the shelving unit, which is a good distance from the door. (00:31:45)
Continuity mistake: After Frenzy uses the POTUS mainframe aboard Air Force One, when he kills the third agent the man falls backward towards the back wall, but in the next shot as the other agents arrive, the body faces the opposite way. (00:32:05)
Continuity mistake: When Sam pursues Bumblebee on his bike, as he is on the phone with 911 there is a close-up of Sam's feet pedaling. After Bumblebee breaks through the gate, there is another close-up of Sam's feet pedaling, but now the gears/chain are different. (00:33:50)
Continuity mistake: In the scene when Sam is being chased by two dogs and is led into a strange-looking place, when Sam climbs on top of a barrel, notice that the dogs disappear once Bumblebee drives in. Also notice that when Bumblebee drives into that place, he does a 180-degree slide, and in the next shot he's seen circling around Sam. (00:34:10)
Continuity mistake: In the scene where Sam is being interrogated at the police station, the cop catches the drug bottle with the bottom facing up. When it cuts, the top is facing up. (00:38:20)
Answer: Because the Decepticons didn't know where Megatron ended up for the last 100 years. Bumblebee arrived on Earth as a scout to check out for any clues, found the glasses on Ebay, signalled the other Autobots, which prompted Blackout and Frenzy to investigate the base in Qatar, which lead to Blackout downloading the base computers and Frenzy hacking the computers aboard the aircraft later leading to the discovery of Megatron's whereabouts.
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