When Morgan cuts open the sewn-up wound in the infected's belly, the wound changes position after he's cut it.
When the professor is being handcuffed to the chair in the glass cage, his right arm position changes between shots, from resting on the armrest to being tucked behind his back.
Near the climax of the movie when Gina has the gun and meets Morgan wielding the axe with Janet, Gina gets jumped by an infected and kills it. While doing so she shoots her last three bullets and then continuously pulls the trigger again. Each pull making a click sound, when the hammer is triggered. This will not happen with the kind of gun she is using.
They were putting so much efforts and taking all pains, even giving their lives, to get their patient zero so that they can start the process of developing a cure. But, when Scooter gets infected after getting bitten by an infected, and he starts turning, Colonel Knox summarily shoots and kills him. Well. Infected Scooter could have been their patient zero present in the lab itself without having to sacrifice any soldier in nabbing him, and they could started to develop cure for the virus from Scooter's body fluids.
Incorrect. "Patient Zero" means the first human carrier of the disease which Scooter (and everybody else who was bitten by another human) is not.
When running outside, the shadows fall to the left of the characters while the moon is visible in front of the characters.
When the soldier shoots the infected on top of the containers and he falls, the stunt jump bag at the bottom is visible.