The .45 that Cassie's father gives her at the camp only has 1 magazine, and he doesn't give her any more ammo. After she fires the .45 while running on the freeway, the gun makes an audible "click", signifying that the magazine has been emptied and she's out of ammo. After she finds her gun at Evan's house, she pulls the magazine from it and it's fully loaded.
On the freeway, Cassie fires 10 rounds from the 1911. Normal, run-of-the-mill 1911's have an 8-round magazine.
Cassie packs her bag before leaving home, looking at her phone with its polka dot cover before she puts it into her bag. When Sam appears in the doorway, the phone is on the bed.
Cassie loses her brother's teddy bear while running through the woods. When she is in a sleeping bag, the teddy bear is with her.
At the beginning, Cassie is wearing Converse sneakers. Once she enters the gas station, she is wearing a different pair of shoes.
The soldiers are supposed to be Army, but their camouflage uniforms are specific to the Marines, and they have Air Force vehicles. It could be intended as a visual cue that 'something' is not right with the military in the film.
After the EMP attack, cars outside Cassie's high school rolling out of control and collide. Since they were being operated in gear at the time, they should have quickly slowed down, if not lurched to a stop, when their engines' crankshafts stopped turning.
After the EMP attack, the cars crash into each other. But all cars have mechanical brakes which would not have been affected by the EMP pulse.
Near the beginning, during the first wave, when the airplane crashes outside of the school, the sheer explosive force and its proximity to the building should have been enough to blow out the windows.
An EMP would certainly turn off many forms of electrically generated power, but it would not be the primary cause of a plane crash. Modern jets have windmill-type generators that deploy if the plane's electrical system fails. EMPs would have to be repeated, as numerous facilities would not be affected and numerous generators would be turned off. The family later relocates to a camp that has electricity.
Cassie states that there are 300 billion birds on Earth, 75 for every human. As of 2016, there are about 7 billion humans on earth, so 75 birds for every human would be 525 billion birds. Cassie may be referring to the estimated humans left on Earth after the power outage, earthquake, and tsunami.
When the tsunamis are hitting coastal cities, the Tower Bridge in London and Siam Securities in Bangkok are wiped out. London and Bangkok are not coastal cities, but they are low-lying and flood-prone. London flooded several times before the Thames Barrier was built. According to a 2015 government report, Bangkok is sinking, and may be submerged by 2030.
After giving Cassie a lesson in disarming an assailant, it appears that Evan returns the .45 clip without returning the loose, unchambered shell. His hands appear in a normal position when he places a round back into the clip.
Evan Walker said Kent State University offered him a scholarship to study Mechanical Engineering. Kent State's College of Aeronautics and Engineering includes an Applied Engineering program, with a concentration in Mechanical Engineering Technology.
After Cassie fires the last shot from the Colt 1911 handgun, it makes several clicks, as if she had pulled the trigger several times. After the last shot is fired, the slide locks back blocking the hammer, so it would not click. The 1911 is a single-action gun. For a trigger pull to drop the hammer, the shooter would have to either fire a round or manually cock it.
Evan tells Cassie his house is about 60 miles from Wright-Patterson Air Force Base. When she draws the route she plans to take from Evan's house to the base, it begins near Upper Sandusky, Ohio, over 120 miles from the base.
Just before Cassie meets Evan, she walks past a sign for Exit 44 stating 46 miles to Wright-Patterson Air Force Base. While I-75 and I-70 near the base both have exit 44s, the furthest one is 21 miles away.
The film is set in Ohio, but the red clay dirt reveals that it was shot in Georgia.
The beginning of the film is supposed to be set in Northern Ohio, within a few miles of Lake Erie. However, with a few minor exceptions close to Cleveland, the Lake Erie coastline is lightly forested and mostly flat. The wooded parks and hills shown exist much farther inland than a tsunami could reach. Lake Erie is also the shallowest of the Great Lakes.
In the refugee camp, Colonel Vosch tells the adults that The Others can transform into humans, and could be among them without anyone noticing. Cassie was outside when that information was shared. Yet later she writes in her diary that you can't trust anybody because "The Others look like us".
Cassie has no idea Ben Parrish is alive, yet he gets off the same bus as Cassie's brother, Sam, when they are unloaded at Wright-Patterson Air Force Base.
When the squad of kids are sent out at night to kill The Others, they wear black uniforms and move stealthily, but their helmets have bright lights, making them easy targets.
Evan sees Cassie cut off her old bandage, helps her with the new bandage, then asks her if she has a pair of scissors, despite seeing her use a pair moments earlier.
When Cassie's father gives her the .45 Colt pistol, she immediately holds it in a direction that points it towards him.