The formation that Whiskey Task Force forms up in when GORT breaks out is militarily unsound; placing all of the unit's vehicles and troops within a large mass presents a large target area that could be exploited by the enemy.
When Helen and Jacob are in the cemetery, the scene from behind Jacob shows Helen's hand on his shoulder, the next scene from behind Helen shows her hand on his upper arm. The scene switches back and forth several time and as it does, her hand goes from shoulder to upper arm and back to shoulder again.
In the beginning of the movie, when Helen Benson walks into the room of her son, in the background on a shelf you can see an action figure resembling a karate fighter due to its white outfit. However, when Helen leaves the room again, the figure is gone. It is replaced by an entirely different action figure.
When Dr. Benson asks the government agent why the highway is shut down, the car window next to the agent is rolled up and completely closed, as evidenced by numerous rain droplets on the window. When the camera angle changes to show the convoy on the empty highway, that window is now completely open.
No British news service would use the British flag as its banner. The British flag is not widely flown within the country. It's never shown on television; stations feel that viewers already know which country they're in.
As the spacecraft lands, its downward thrust causes a park bench to be uprooted and blown across the ground. That kind of pressure would have sent everyone in the area flying across the ground as well, yet only two people are blown over, the rest of them, even the woman who grabs her child as its pushchair is blown away, manage to stay on their feet.
The door to the flash chamber complex is blown several hundred feet in the air when the Nano robots get out when actually they absorb materials and don't blow things away. The door should have disintegrated as with other things that they came into contact with.
The robot figure intercepts the MQ-9 Reapers and flies them into what is depicted as a M1 Abrams Main battle tank. The destruction depicted could not have happened, even with the missile warheads on-board. The M1 variant tanks have taken hits from "explosive" tank rounds in combat with only minimal damage to their advanced armor composites.
The colonel commands the controllers of the MQ-9 Reaper to fire their Sidewinder air-to-air missiles at GORT in his robot form. The Reaper carries only GBU-12 Paveway II or AGM-114 Hellfire II air-to-ground missiles. Considering the situation, the most likely payload would be the Hellfires. In addition to this, when we see the drones in flight, there are no Sidewinders visible on the wings; only what appear to be Hellfires.
'Sidewinder' missiles are fired at GORT while in robot form and in insect form. AIM-9 Sidewinders are heat seeking, air-to-air missiles, targeting objects on the thermal scale of jet engines. There is no suggestion that GORT is emitting a heat signature on that scale in either of his forms, and they would not have been used when GORT is in his robot form, as he is on the ground.
A tandem-rotor helicopter can be seen transporting scientists; it is a CH-46 Sea Knight, used the U.S. Marine Corps, but it has 'United States Army' written along its side. The Army has never used Sea Knights, but uses CH-47 Chinooks, which are very similar visually, but can be distinguished by its large engines at the back, which the Sea Knight lacks.
The M1A1 Abrams tank that one of the drones taken over by GORT lands on is a U.S. Marine tank, as evidenced by the 8-barreled smoke grenade launchers on the side of the turret that was used only by the Marines. The crewman seen jumping off, however, is wearing an Army uniform.
In the sequence when the world's electricity is "neutralized", the shot of London, showing stopped traffic around the Thames River, there is clearly a motor boat moving up the Thames and out of the shot. If all of the car engines were stopped, the boat's engine would also have been stopped, too. This same error occurs in the original film.
Nearly all U.S. soldiers seen in the film are wearing Interceptor Body Armor (IBA) shoulder protection pads when in combat gear. While American troops did wear these, the shoulder pads were never as widely used as is depicted onscreen; most often, troops only wore the IBA vest.
Compositing/3D modeling error: After the helicopter lands in central park with the scientists the camera pans counter clockwise around the rear of the helicopter you can see on the left rear landing wheels the aircraft appears to slide to the right over the ground.
Even though it is 2008, Klaatu's ship, being identified as "object 07/493" and "discovered just beyond Jupiter's orbit" could have been discovered in 2007 because, as Michael said, "At first, it was projected to pass millions of miles out of Earth's orbit."
When Klaatu, Helen, and Jacob leave Professor Barnhardt's house, Klaatu asks to be driven to a location where he can retrieve one of the smaller spheres. They travel to "Highlands, New Jersey", stop in a forest, and Klaatu raises the sphere out of a swamp. Highlands, New Jersey is a sandy, beach-front community in northeast Monmouth County, right on Raritan Bay. It has no forests, and no swamps. However, the Highland region of New Jersey is a mountainous region west of New York City, encompassing parts of Passaic, Sussex, Warren, Morris, Somerset and Hunterdon counties. The region is heavily forested and it is likely this is the location/region being described in the film.
As soon as it was discovered that the object was not following a gravitational freefall trajectory, it would have been known to not be a natural object. However, the make-up of the science team that's been assembled (including a civil engineer) suggests that the plan is more for dealing with First Contact than physical aftermath of an impact, suggesting that they are quite aware the object is Alien rather than natural. After all, if the scientists had been gathered only to deal with the aftermath, then they would have been gathered at a location a safe distance from the predicted landing site.
As Dr. Benson arrives at the facility, a soldier is depicted carrying a .50caliber MG on his shoulder, up a small incline. Although possible, it is unrealistic due to the extreme weight (85lbs) with the barrel inserted. Under normal operations, the barrel is inserted only after emplacement/mounting of the weapon system. However, the .50 cal. machinegun is regularly carried as shown, but rarely for long distances (and, for a fit person 85 lbs. is not an "extreme weight").
Vladimir Putin appears in the global reaction videos, yet he had left office by then. He is still the Prime Minister and de facto ruler of Russia, so Putin making official statements about an international crisis is believable.
When Helen follows Klaatu into the forest, she leaves Jacob in the car, telling him to lock the door. As instructed, Jacob locks the door. Problem is, the car has 3 other doors which he does not lock. However most modern (post-1980s) cars have a feature called "central locking". At a minimum, all the doors are locked/unlocked if the driver's side lock is operated.
When the mother ship lands in the park, the shadows of approaching people shrink. One would expect they should lengthen, since the light is descending. However, if the light is coming from within the sphere, and it is approaching people not from directly above, but horizontally, shadows would appear to shrink.
As the helicopter lands to unload the scientists including Dr. Helen Benson (Jennifer Connelly) in Central Park, the rotors don't seem to be creating any down-wash as evidenced by the dead leaves on the ground. They're completely motionless around the helicopter.
(at around 1h 08 mins) When the television speaker announces the latest news that there was riots in "London, Chicago, and many cities in China", on the screen you can see some vandals breaking stores, police on horses, and the third video is not from listed cities, but from Belgrade (Serbia). They used a historical event which occurred on 5th October 2000, when 500,000 demonstrators set the Parliament building on fire. On that day, Slobodan Milosevic was overthrown from power.
When Klaatu is in the car healing the incision on his chest, Helen watches in amazement. The incision was on his left side and he pulled his shirt and jacket to the left in order to apply the placental balm. With Helen driving, sitting on his left, there was no way possible for her to watch any of this.