After kill #4 when the cop is chasing Jonas, the street he turns down is clearly a one way street. If you look all of the traffic lights are facing the wrong direction, they are facing Jonas and not the direction of traffic.
Between scenes, Allan's bruise changes in size and color.
As Allan is driving to the Rosen building he pulls up at the lights to turn left, behind a black Honda. The camera then pans out to view him behind a white truck instead.
At the end, while carrying his wife, his shirt is smeared with blood stains by her wife. Later when he accompanies her into the ambulance, the back of his shirt is clean.
When the police car pulls up outside Mike Dodd's apartment the officer in the driver's seat checks the police scanner. His right shirt sleeve is seen rolled up. In the next shot which shows him getting out of the police car, his sleeves are rolled down.
When Allan Campbell was sitting in the bar he asked the bar attendant if he could have a bigger glass. The bar attendant replied "nope, its the biggest we use" yet Jonas Arbor was sitting beside Allan and clearly had a much bigger glass.
When the bartender tells Allan "That's the biggest glass I've got, sorry", he is most likely referring to the glass as the largest glass in which he is legally allowed to serve a straight-up alcoholic beverage. The other glass contains only water.
(at around 1 min) Allan enters an elevator in the Rosen building and uses it to go up to try and catch Brian #4 on the hit list. The elevator has a sign inside with the floor numbers on it with a light highlighting the current floor. This sign is clearly missing 13, going from 12 directly to 14. In the next scene you see Brian, #4 on the list standing outside the elevator waiting to go on. The camera shows the sign above the elevator on the outside which does show a 13 but the light is illuminating the 14. It is not uncommon for buildings, especially older ones, to not have a floor designated as 13 but as building and offices are updated with newer signage it is possible, and very likely, that the outside sign does not match the inside sign and would simple skip over the 13 even though it is present and go directly to the 14. Oddly enough, the reason that many older buildings, and even some newer ones, have no 13th floor designation is because of the superstition about the number 13. Of course there is still a 13th floor so any negative influences would still be in effect regardless of what you call it.
When Alan spills coffee on his shirt, the stain appears dry (dark edges, no transparency).
After Jonas kills #4 and forces Allan into the black Cadillac, they speed off with the police in pursuit. In the early scenes, you'll notice the black Caddy does not have a front license plate, but after the Caddy crashes into a vehicle and has a smashed front end, there is a license plate on its front.
37 minute mark: When Alan is driving, the camera shot from the inside of the car shows Alan in the leftmost lane behind a dark Civic but the outside shot places him in the second-from-the-left lane behind a white pickup.