Character mistake: The fetus' blood type was AB and the mother had a known type of A. So Dr. Huang said the Father had to be type B which is not completely true. The father could also be type AB as long as he had a single chromosomal copy of the B allele, which any doctor would know. During meiosis only half your genetic DNA is passed on to the offspring.
Revealing mistake: When Amanda and Fin are in Atlanta following up on their rape case they walk past several cars with visible Georgia license plates mounted on the front. Georgia is a rear plate-only state, and wouldn't have had plates mounted on the front of the cars as shown here.
Deliberate mistake: When James is shot on the courthouse steps, the crowd of reporters that has gathered quickly scatters to escape the gunfire. One of them is a woman in a black windbreaker holding a camera. The camera cuts away briefly and then back to the crowd - you see the exact same people, including the woman in black running in the exact opposite direction as before. The footage was apparently mirrored and repeated for the second shot of the fleeing crowd.
Revealing mistake: In the scene where Detective Munch visits the hospital room of a young comatose girl for the first time, we see that the girl's left arm is alongside her body above the top sheet. As Munch approaches the bed, we now see that her arm is below the top sheet. When Munch visits the still-comatose girl a second time in the last scene of the episode, we can see in the foreground as he is entering the room that the girl's head is turned, facing her right. As he pauses to watch her, we then see in the next shot that she is now facing upright towards the ceiling. In this same shot, you will also notice the purportedly still-comatose girl slightly move her head and lips as if swallowing.
Continuity mistake: When Benson and Stabler are interviewing Virginia at the end of the episode, when she admits to committing the crime, she breaks down into tears and her face turns red. The next shot is from over her shoulder, and her expression is normal. In the very next shot, from the front, her face is flushed and tears again.
Factual error: Season 11, episode 2 ("Sugar"). When tracing the "Master Baiter" the detective says she can't trace the subject because "the HTML code is scrambled". There is no such thing as scrambled HTML, and on top of that HTML can never give away any information about a subject's location. Also, she can't get his IP address because it constantly changes. Yet, she does know from what exact wifi-spot he connected. If you get random IP-addresses, for instance by using random proxy servers, you can't pinpoint a location (which was of course why he used this technique).
Factual error: Season 9 episode 18 (TRADE): The scene where Pierson Bartlett is on the stand, he pulls a spoon out of his jacket. This would never be allowed. He wouldn't get through the metal detector with any metal that could be used as a weapon. He would either have to take it back to his car, or leave it at the security desk.
Continuity mistake: Season 11, Episode 3 "Solitary": When Donovan pushes Stabler off the roof, Stabler is standing with his back facing the parapet and goes straight over. However, when he's shown on the roof below after he's landed, he's turned almost a full 90 degrees and is lying parallel to the building.
Factual error: The way that the drug Scopolamine is described is not accurate. It does not render the victim "unable to resist instructions". It can produce "twilight sleep", delirium and euphoria, but does not give anyone complete control over another person as depicted in the episode.
Character mistake: When Casey is talking to Rebecca Balthus about Jennifer's defense, Balthus claims that Jennifer is innocent and intends to prove it. While she can present a defense, Balthus is not required to prove anything: the burden of proof lies solely on Casey; Jennifer possesses what is called the presumption of innocence, the basic principle that she is considered innocent until it's proven she's guilty.
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Continuity mistake: When Stabler steps out to confront Tarzi, there is a long, brown brick wall to Tarzi's right. Tarzi then turns and runs across the street and is followed by Fin. Munch steps out and yells "halt!" There is another shot of Tarzi and he stops again. Right before he is tackled by Fin, behind him, to his right, is the same brick wall as before even though he crossed the street and ran down the block.
Character mistake: At the end of the episode, Abby Carmichael says that professor Rousseau will be convicted of three class-A felonies, with a term of a year each. According to NY state laws, three class-A felonies would lead to the death penalty; Abby meant to say three class-A misdemeanors.
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Continuity mistake: Benson visits Stabler at his home to confronts him about the FBI detail he has ordered to protect her. They talk outside and then Benson is seen walking away. The next shot shows a side shot of Benson approaching him again in silence but mouthing words to him.