On the train in the beginning, when Andy is looking at a map, the picture at the top of the map changes between shots. First, there's a little land and a lot of water at the top, then there's all land at the top.
After fighting the werewolves in the crypt, Andy goes back to the house and he has a cut on his right shoulder. However, when the werewolves turn up, he runs down the stairs and the cut has now disappeared.
Andy is in hospital bed after Brad and Chris went looking for the suicide note, he supposedly sees "the mystery woman" in nurse garb walking down the hallway. When Andy gets out of bed to chase her, and is in the hallway, all the rooms windows are covered with frosted glass.
When Serafine transforms into a werewolf, her knees fold backwards to become the werewolf's hocks (the equivalent to the human ankle) and her upper leg bones bend forwards to become the werewolf's stifles (the equivalent to the human knee). However, humans and wolves have very similar leg structure, so there was no need for any of her joints to change, and she could have become a werewolf with just a lengthening of the bones from her ankles downwards. As it is, she will now have an extra joint in each leg.
When Andy is fighting Claude on the subway train, Claude is supposed to be naked after transforming back to human form again, but in several shots during the fight you can see that he is wearing pants.