Character mistake: After the murder that takes place while the team is at the church meeting, they gather together to talk about narrowing down the suspect list to the people who didn't show up to the meeting. Spencer shows up with a stack of papers and says 18 suspects didn't show up. We then see his actor break character and almost laughs when he looks over at Ashley, whose actress too almost breaks character from laughing.
Character mistake: Art expert Dale Kingston describes Goya as 'the penultimate artist'. "Penultimate" has nothing to do with greatness or artistry, it means second to last, and nowhere during his speech does he indicate that Goya is 'second to last' in anything to do with the discussion. In the context he uses it the word is completely meaningless.
Character mistake: As Reddington sets up the blood transfer between himself and Ressler he inserts the intravenous line in Ressler's arm first and then in his own arm. This way the remaining air inside the line gets into the recipient's body and could very well kill him. Judging the expert way he handles the set up he should know to first insert the IV in his own arm, let the line fill with blood and then insert the IV in Ressler's arm.
Character mistake: When Mac, Stella, and Danny are trying to determine where the fired bullet entered the train car, none of them are wearing rubber gloves. But even though they're not handling any evidence, they're still processing a crime scene. (00:05:00)
Character mistake: Seven minutes into the show, Sarah Sidle is about to do an internal sexual assault exam/kit on an unconscious victim in the hospital, Sarah picks up a metal speculum and says aloud to the victim (in a presumed moment of empathy), that she "never really liked this part of my yearly exam. These things are always freezing" referring to the speculum in her hands. She then brings a speculum to her mouth and begins to blow open-mouthed on it two times, forcing her hot breath on it to warm it. She then begins to insert it into the victim as the scene cuts away. This is pure stupidity, as no trained CSI would ever contaminate the tool like this. Sarah just added her own DNA to the speculum via her breath so any saliva or body fluids are now on the speculum what she is about to use on this patient, who is now also exposed to any STDs from Sarah.
Character mistake: 23rd minute. Jack meets the female assassin in Anderson's apartment. She demands that he show his credentials. Jack says he's with CTU on a provisional basis and therefore he has no badge. The agent that came with Jack confirms that. Yet, in the 13th episode (minute 14) when he enters the sports shop with Audrey's husband, he shows his CTU badge to the owners in order to prove that he in fact is a federal agent.
Character mistake: When Olivia and Dr Galina are in the bathroom, Galina mentions an umbilical chord, from a baby whose mother died (Nadia), that contained Olivia's mitochondrial DNA. Mitochondrial DNA comes from the mother, so Nadia's Mitochondrial DNA came from Letha who got hers from Marie, absolutely nothing to do with Olivia.
Character mistake: At the end of the episode, after Sarah has been tricked into revealing her plan and is rather obviously going to go to jail, Tru tells her that she "should have taken half," meaning that she should have settled for half of Andrew's money in a divorce instead of trying to get all of it by having him murdered. But Tru seems to be forgetting that Sarah has been trying to divorce Andrew all along, and it's Andrew who has stood in the way of that. Sarah would evidently have been perfectly happy with half, but Andrew prevented it from even being on the table for her, so Tru's comment doesn't make any sense.
Character mistake: Tom Mason makes references to smaller armies defeating larger ones, of which history is rife with examples. He cites the Scottish defeating 'the British' at the Battle of Stirling Bridge. 'The British' did not exist at that time. The Scots administered a beating against the English in the Scottish War of Independence, against the Earl of Surrey, under Edward I. Someone with his level of knowledge would know that.
Character mistake: In Brian's "Laws I Have Broken Since Joining FBI" list, item #30 misspells the word "recorded" - "30) Recoreded NFL Game Without Consent." He'd only have that knowledge if he was using NZT, and if he was, he wouldn't make a mistake like that.
Character mistake: When Kim is trying to convince Lisbon to help the FBI on their case, she says Jane stopped the ten-year reign of a mass murderer. Red John was a serial killer, which, by the FBI's definition, is a criminal behavior distinctly different from mass murder; he may have had a large number of victims, but he killed them either one or a couple at a time, with a cooling-off period in between, not all at once.