When Tommy and Jennifer are in the safe room, Mars smears a bloody hand print on the window and shoots the window three times, but when Jeff comes back to get Jennifer and Tommy, the hand print is less smeared and the bullet holes are not in the window.
One of the hostage takers hits Walter Smith in the forehead, causing him a large contusion and bleeding. When Smith gets to leave his house and is put on a stretcher inside the ambulance, you can clearly see that there is no sign of injury where his contusion is supposed to be, and no blood either.
When Tommy cuts the tape around his hands at his bedroom, the piece of glass he uses has cut his hands open, wounding his hands and covering them in blood. However, when he crawls through the ventilation shaft, he doesn't leave any traces of blood behind even though he needs his hands to crawl through the shaft.
In the very last scene, as Talley and his family leave the old club and head for the ambulance, someone can be seen upper left walking out of the frame, head down, baseball cap on. When the camera pulls back, there is no one here.
During the hostage negotiation in the beginning, Talley writes a message on the whiteboard and then tosses it to his friend. He tosses it white side down, but it slides over to his friend white side up.
The goof items below may give away important plot points.
In the end scene, in the old hotel, one of the kidnappers points a gun at Talley. Talley has taped a gun to his hand - in one shot the hammer is cocked, in the next it isn't, then it the next shot it goes back to being cocked.
When Talley & Smith get out of the ambulance where Talley's wife & daughter are being held, Smith has a bandage on his head. After the rescue, we see Talley & family enter the ambulance. As the ambulance begins to pull away we catch sight of the driver, who is wearing a bandage around their head. The driver of the ambulance was indeed Smith.