In the final battle, Joel can be seen walking towards Jacob like a zombie in the background when Jacob asks if Saga is alright. The camera cuts to Saga for a brief moment. When it cuts back to Jacob Joel is not there.
The blood on John's mouth increases between two shoots. After having fallen, he has much more blood on his mouth than before he fell for no reason.
John's position after falling down changes. First, he is right outside the house when falling. When he raises up again he is much closer to the police.
Why didn't the other soldiers in the cabin turn into vampires? Two were bitten and were not seen burned by the survivors.