Factual error: When Dexter and Doakes are looking at the severed foot wearing a soccer cleat, Dexter states, "The foot was severed between the tarsus and the metatarsus." However, the foot was severed proximal to the tarsus, through the tibia and fibula. The cut was easily too high to be between the tarsus and metatarsus. (00:16:45)
Continuity mistake: When Doakes is about to be killed by Guerrero, the police save him by shooting Guerrero, giving him a bullet wound on his right shoulder. He is also cuffed on the ground to be arrested. However, when he is pulled up, Guerrero does not have a bullet wound anymore.
Factual error: In the police report Dexter examines, Emmett Meridian's name is followed by PhD, and yet he is referred to as a psychiatrist and prescribes medication. A psychiatrist would have an MD after his name, and a psychologist (PhD) cannot legally prescribe meds.
Factual error: When Dexter is in the hospital as a child, the doctor says that Dexter has a very rare blood type, AB negative. Although it's very rare, the people with AB- can receive donor blood with A-, B-, AB- and 0-. AB- is a very good blood-type when you need to receive blood. While it is true that hospitals normally have to use AB- because of the complexity of other proteins (and to prevent adverse reactions), in case of an emergency, like Dexter's, and a shortage, a hospital will use a blood type close enough to not likely cause a reaction. In this situation, the hospital would give Dexter O-, B-, or A- instead as blood loss would normally kill a patient long before a suitable donor could be located, called in, admitted to the hospital, and have the transfusion set up. (00:31:00 - 00:32:00)
Factual error: Dr. Meridian's victims are suicidal following withdrawal of an antidepressant, begging for more, and Dexter refers to the doctor getting his patients addicted to antidepressants. This reflects a disappointing and fundamental misunderstanding of the science of antidepressants. Even those that have "discontinuation syndromes" do not produce mood swings this wild. It is possible (though unlikely) that a random individual would have this reaction to discontinuation of an antidepressant, but Dr. Meridian would need to be in control of his victims' descent, to be sure they would become suicidal so that he could suggest the use of a gun and be sure their suicides would be successful. There are no mainstream antidepressants that would produce this effect upon withdrawal.
Audio problem: When Deb tells Angel to "look up" warning him of the security camera, Angel moves his lips as though he's talking but there is no audible dialogue. A few seconds later, his lips stop moving but then his audible lines are spoken. Then, again, there is no dialogue, but his lips move again. (00:07:15)
Factual error: When Dexter is reading the list of drugs found in the autopsy of the murder victim, one listed is "Cialopram." This is a misspelling of the antidepressant Citalopram; misspellings do not occur on drugs lists in toxicology reports, as they are computer-generated. (00:37:10)
Other mistake: When Dexter is running Matt Chambers' fingerprint though his computer, he brings up four newspaper articles where the names Matt Brewster and Matt Rasmussen are used. In the final article, the headline reads "Matt Rasmussen of South Boston arrested", but the body of the article uses the name Matt Brewster exclusively. Other than the first few words, the text of the final article is identical to that of the previous one. (00:33:50)
Continuity mistake: When Doakes asks Deb "what took her so long" arriving at the first crime scene, Masuka is stood next to him. However, over the course of the conversation Masuka is seen in the background talking to another group inside the house, and in the next shot he is standing back next to Doakes. At the end of the conversation he walks over to the group inside the house. (00:05:30 - 00:06:00)
Continuity mistake: When Dexter and Deb are celebrating her promotion, just before they toast and you look at them from the side Deb has her hands free, when the camera changes she has a crab leg in her hand, and when the camera changes again her hands are empty once more. (00:46:45)
Other mistake: Doaks says he saw the man's gun and chased him, lots of questions arise about what happened, but no-one mentions how a cop has no right to ask a person about a gun they have on them without probable cause. Doaks has no reason to even go after the guy.