Continuity mistake: In the scene in the interrogation room with the two programmers there is a big plate of doughnuts which the hacker eats very quickly. But take a look at the plate between shots when he's talking and you'll see that the amount of doughnut left on the plate varies greatly: Sometimes there's one whole doughnut left, other times, in the same conversation, there's only crumbs.
Continuity mistake: After Sam and Mikaela arrive at the Griffith Park Observatory (the planetarium closed for renovation), when they start to hold hands the distance between the two of them changes from farther apart, to close together, to farther apart. (00:59:35)
Visible crew/equipment: When Sam rushes to his waiting father after class and tells him about the A- they drive off. In the next close-up shot the filming vehicle, with its top mounted crane and camera at its front end, are reflected on the car's surface as they drive past, before pulling into the Porsche lot. As this shot continues, when they drive onto the Porsche lot, the filming vehicle directly behind them (note its headlights), is reflected on the large windows in front of them and when Sam is told he isn't really getting a Porsche the filming vehicle, which is now beside them, is reflected on the window to their left. (00:11:45)
Visible crew/equipment: When the base in Qatar is attacked, in one shot two crew members, one with a camera, can be seen towards the left side of the screen. (00:06:55)
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)
Revealing mistake: A yellow Pontiac GTO gets shot up, then gets blown in half with the rear end landing inside a shop window. If you look at the sideskirt of the car before it gets destroyed, you can see the cut already in the sideskirt where it will split apart. (02:01:20)
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)
Visible crew/equipment: When Sam is at Bobby Bolivia's cars dealership intending to buy the Chevrolet Camaro and all the cars' windows explode, as the camera turns around a shocked Bobby Bolivia the shadow of a boom microphone is visible on his face.
Continuity mistake: At Hoover Dam, when the soldiers salute Keller the clock reads 10:00, then as Keller, the soldiers, Maggie and Glen walk away in the background, when Simmons tells Sam that they got off to a bad start the clock reads 11:35, and next shot when Banacheck interrupts it reads 11:43. Also when Simmons talks to Mikaela and Sam the word "Nevada" is gone and it only reads "Time" under the clock. Then when Banacheck says, "Come with me, we'll talk about your car," the word "Nevada" is back under the clock. (01:35:25)
Continuity mistake: When Prime lifts Mikaela up to Sam's bathroom window, there are two baseballs in acrylic display cases and another object (looks like a vintage camera) on the windowsill (beside the tub). Then when Sam runs to that window and sees the Autobots parked as if it were a "truckstop", all those items disappear and are replaced by two small overturned flowers pots. (01:11:55)
Continuity mistake: While standing in front of a frozen Megatron, after Banacheck explains that Sam's great-great-grandfather made one of the greatest discoveries, Sam and Mikaela are shoulder to shoulder, but in the next back shot they are 4-5 feet apart. They're beside each other again in following shots. (01:37:20)
Continuity mistake: When Mikaela has Bumblebee at the back of Mike's Towing truck, she drives down an alleyway, and when she stops the truck in the close-up there is a trashcan and other debris between the front two tires, which vanish in the wideshot. (02:02:25)
Continuity mistake: When Agent Simmons takes Mikaela and Sam into custody, the headrests in the SUV vanish when Prime shows up. The driver's headrest is visible just after they enter the car. When Sam says, "My car had been stolen, from me, from my home," and when Simmons asks, "What do you kids know about aliens?" the headrest behind Sam is visible, among other moments. (01:19:00)
Continuity mistake: When the troop is flying in the helicopter at the start of the movie, Epps is not wearing sunglasses. When it cuts back to him, he is, then again it cuts away and back several times and you can see an indentation on the side of his head where the Oakley sunglasses were.
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: 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: When the SUVs arrive at the Hoover Dam, the lead car pulls up to the curb and the doors open directly in front of the first elevator tower (there are four, which are seen in overhead shots), on its right, with the two Nevada intake towers well ahead of the SUV, on its left. Next close-up, however, as Sam exits the SUV the vehicle is now parked farther up the road, directly in front of the Nevada intake towers to its left and closer to the second elevator tower. Note the yellow pedestrian walkway markings (leading to the Nevada intake towers) the SUV is parked on in the second shot. (01:34:25)
Continuity mistake: When Sam grabs his mom's pink bike, there is nothing in the white basket at the handlebars as he flees from Bumblebee. However, at the start of the shot just before the tire hits the broken concrete, a square pink pillow suddenly appears in the basket, before flying out as Sam flips over. (00:48:10)
Continuity mistake: After Sam knocks Mikaela off her moped, they are both on the ground right beside the moped when Bumblebee shows up, but in the overhead shot as Sam helps Mikaela up the moped is gone, not moved, just gone. (00:51:15)
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)
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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