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: 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: Happy determines that the nitrogen hydroxide ate through the drum because it was "steel alloy," in contrast with Walter's requirement that it be "pure steel." These terms are inaccurate, and would not be used by technical experts like Happy and Walter. Every steel is an alloy, combining at a minimum iron and carbon; steel with other alloying agents is called "alloy steel," not "steel alloy." Because steel doesn't refer to one specific substance, "pure steel" could never be used to specify a material for a given application.
Character mistake: Captain Janeway states the temporal differential ratio is .4744 seconds per minute (meaning for every minute on the surface, only .4744 seconds pass on Voyager). Tuvok calculates that 30 minutes on Voyager would be 2 days 11 hours and 47 seconds. However, at that ratio, 30 minutes would be 2 days 15 hours 14 minutes and 15.9 seconds. Later Tom (who was on the surface) says the last two months for them was only 2 days for B'Elanna (who was on Voyager). But with the temporal differential, 2 months on the surface would be less than 12 hours on Voyager. 2 days on Voyager would be almost 253 days (almost 8.5 months) on the surface.
Character mistake: Trivette hands the man in yellow a bullet recovered from the plane Walker and Alex were traveling on, which was shot down by an assassin flying a P-51 Mustang. This man, and later Trivette, mistakenly refer to the round as a "50mm," when in reality, Mustangs were equipped with M2 Browning .50 Caliber (12.7 mm) machine guns. (00:30:25)
Character mistake: Days after Drew's death (Roy and Johnny had two days off after Drew's death), during the meeting that Brackett has with the four paramedic units, one of 59's guys asks, "What do we do when we have this overload situation on the same frequency? Two squads, like 51 and us today?" The situation with the frequency did not happen "today" as he said, it happened at least three days prior.