During the runaway streetcar scene, the power is cut to stop the streetcar. We see the lights go out in the city in a night scene, but when the passengers disembark afterwards, the sun is still shining. Then moments later, it is pitch black out again.
You can tell the scenes that had to be re-shot later by looking at John Cena's neck. In the original shoots he doesn't have a scar on his neck and in the re-shoots he has a scar from his spinal surgery. (Cena talks about this on the commentary of the movie.)
Whilst the FBI car is trying to stop the runaway street car, one of the scenes shows that the front wheels of the car are not moving, almost as if the car itself is attached to a railway wheel set or bogie and that the smoke is not coming from the tires.
Danny is running on foot and by simply cutting through houses and backyards he is able to cross the path of the same speeding car several times. Unless the speeding car is doubling back on itself over and over again, this feat is totally impossible.
When the girl got hit straight on by a truck. Laying on the pavement with blood on her face, some of the blood was dried blood; Dark black dried blood after only seconds.
Willie dies because the elevator cable exploded with a bomb. Any elevator that is allowed to operate must have mechanical brakes that engage automatically through inertia if an elevator were to fall unexpectedly.
Non-Olympic swimming pools are about 9-10 feet deep at its deepest, and Danny and Molly jumped out of the helicopter towards one and a height of a couple hundred feet. Both of them would've been either killed or crippled on impact.
Danny tried to cut power by hitting or hammering on the electrical connection on top of the street car with his gun. Street cars operate on high voltage. Just touching this exposed connection with any part of his body or any conductive object in his hand would have electrocuted him instantly. Rubber or leather shoes cannot prevent high voltage from easily passing through one's body.
The helicopter explodes almost directly over the rooftop swimming pool. A lot of the money from the helicopter flutters down to land in and around the pool, but none of the wreckage lands anywhere near it.
Defibrillators give an instant jolt at high voltage, not a taser-like continuous current as shown in the movie. ("Extreme Cut" only)
During the streetcar chase, Danny uses his pistol to repeatedly shatter the car windshield before removing it and exiting, rather than simply climbing out of the door.
EDIT:
Exiting through the door of a car, being pushed by a speeding streetcar, wouldn't have been feasible under ANY circumstance. The windshield would have been the safest and most stable route to get inside the streetcar.
When Danny's house explodes the force from the blast throws Danny across the street, the blast didn't knock over the surrounding fence or a bike leaning on the fence.
At the end of the foot chase, when the car hits the boat on a trailer, the car launches into the air well before it strikes the boat.
Danny cuts off the power and the wagon stops but the lights in the wagon are still lit.
(at around 59 mins) After the elevator drops down and we see a shot of Fisher hanging from the window in the shaft, the leg loops of his harness are visible though his jeans.
Throughout the opening sequence, the people speaking over the communication net are not pronouncing street names properly (Ex: "Conti street" should be pronounced Cont-eye.
When Danny and Agent Aiken are checking Security Footage to find Miles, when they spot him, a security guard pauses the footage, however, 1 moment later, Miles is seen writing on a sheet of paper in the footage, but no one unpaused the footage.
While Detective Fisher is driving through the city in the fire truck, continually while the horn is blazing he is not pulling on the line that makes the horn noise.
(at around 30 mins) When Officer Fisher is chasing the suspects on foot in the car after his friend gets shot in the butt, he runs through a house, then jumps over the fence in the backyard. Once he lands on the other side of the fence, you can see a cameraman's shadow very plainly being projected onto the fence.
When talking on phone after the house blows up you can see a police crowd control officer in the background standing in front of an orange car.
The FBI Agent standing in the police van upon spotting terrorist Miles Jackson claims that Jackson was responsible for the bombing of the American Embassy in Frankfurt. In fact, the American embassy is located in the German capital city Berlin.
As the character Danny Fisher along with his brother are entering the building on fire they pass a fireman breaking the window of the housing to a wall-mounted fire-hose. These are supposed to be unlocked and the doors should allow themselves to be opened 180° - any fireman would know this.