When the doctor is murdered, the killer makes an incision on only the right side of the throat, but when the body is discovered it's been slashed, very crudely, all the way across.
There is no beard on Lukas's face when he talks Mara out of leaving, but in the next scene (presumably taking place just after it), he has.
When Mara and Lukas arrive at their destination after the dance, the car stops and they are seen talking, but in the very next shot they are not.
When Carlo supposedly hits the man following Mara at the end of the movie, he doesn't look anything like Carlo.
Near the end of the movie, when Mara hangs up and leaves the room, obvious cut can be seen to the next shot when man is walking around the house.
When first victim is killed, it is obvious that there is no cut, but just a line of red paint dragged on a victim's neck.
When first victim is discovered by a woman, you can clearly see the man still breathing.
In the scene when Lukas remembers where he saw Esmeralda, you can see something on a camera at the bottom right. From then it appears throughout the scene.