Other mistake: Pretty much everyone in the film, especially Alice, seems to be able to fire their weapons without reloading at all.
Continuity mistake: When they enter the "cargo hold" on the Arcadia and the light turns on, the camera shows the room is empty and completely white. When Alice reaches the other end a few min later there is a blood trail along the floor into another room.
Continuity mistake: During the scene on the rooftop, after shooting some approaching zombies, the group run into the lift while shooting a bunch more zombies. The bomb then explodes, sending the lift down. The scene goes back to Alice fastening herself on a sling. When the camera moves to show the zombies, all of the zombies have moved back some 25 feet away and all of them are standing still, waiting patiently for Alice to make the next move. Alice turns around to run to the edge of the building, and we can see that the zombies who had been shot earlier and should still be lying around have magically disappeared.
Continuity mistake: After Wesker flees Arcadia in the Umbrella chopper, though he himself has the ability to heal extremely quickly, his clothes no longer have bullet holes in them.
Continuity mistake: Bennett stabs Alice in her lower arm, from the top to bottom, probably between the bones. But in the revolving shot which reveals Wesker, the knife is suddenly facing side to side, meaning the knife would be going over the bones.
Revealing mistake: After Bennett takes off, Luther jumps on the edge of the prison. When he hits it, you can see the seemingly solid concrete edge wobble.
Factual error: The blood stream on Wesker's head is wrong. He is leaning over to his right, and the blood coming straight out of the wound is going slightly to the right, and then straight down, so far so good. But at the angle he is lying, the blood should have stopped at his eye, and even if it did jump over his eye socket, it should have been directly below or even more to the right of where the first stream ends.
Continuity mistake: After the Tower Swing, Alice lands where she started out: in front of the garage with the UPV. Note the sign with the gun on it. But the door right next to it is closed. Behind that door is the UPV. Since everybody was in somewhat of a rush, it doesn't make sense that anyone should have closed it.
Continuity mistake: Alice is in the shower and draws her gun from the holster on the pole. She takes a couple of steps forwards, camera cuts, and she's suddenly much further forwards.
Continuity mistake: In Extinction, we see Kmart be handed the Alaska book and say "You're not coming?" to which Alice replies "Take care of the others." In the flashback seen here however, Alice replies "Take care of the others, Kmart".
Continuity mistake: In the after titles sequence, when Jill is addressing the group in the plane, she is walking with her hands on her back. When she turns around, heading towards the tail, in the long shot her hands are on her hips.
Continuity mistake: Alice stabs Wesker in the head with the handle of the scalpel tilting over to Wesker's left side. In every shot afterwards, it's facing to Wesker's right.
Continuity mistake: In the front shot of Alice just when see jumps off of the roof, in the far right corner of the screen, one of the zombies trips and falls down. But in the wide-shot directly afterwards, that zombie is instantly gone.
Revealing mistake: Just after the Tower Swing, Alice shoots with her Smith and Wesson at a load of zombies. But when she fires the last two shots (the ones in slow-motion) pay close attention to the gun in HER right hand. The chamber doesn't start to turn until after she has fired the shot, meaning that the hammer would strike a spent bullet.
