Continuity mistake: When Lumen stabs Dexter with his knife in the swamp, she hits right above his elbow which he grabs promptly. When the camera angle changes, he's now grabbing his upper arm that's bleeding from a different spot than where he was stabbed.
Character mistake: Searching for clues to identify a suspect, Masuka takes fingerprints from the interior of a truck. Back at the lab, he says he had two dozen prints and they all belong to the same person. Unless the prints are all of the same FINGER, there is no way he could know the prints were all from the same person without a suspect to compare them to. Masuka is a forensic expert and should know better.