Continuity mistake: As the detectives are talking to their captain about the bank robbery, in a shot from behind the captain he takes his hands off his food and clasps them in front of him. The shot cuts to his front as he starts talking, and he moves his hands and clasps them again.
Revealing mistake: Walter accesses code on the sick girl's laptop to trace the source of the virus - aside from the fact that the code comes straight up a fraction of a second after his hands even touch the keyboard, the code displayed in the black window is for a set of traffic lights, with lines like "Walk/Dont_Walk" and "Green_Arrow/Yellow_Slow." (00:08:10)
Continuity mistake: Most of Season 1 takes place in January of 2006, while Season 2 takes place in March of 1979. Molly mentions near the beginning of Season 1 that she's 31, and her father confirms this in episode 10 by mentioning that she was 4 years old during the events of the Sioux Falls massacre (season 2). In season 2, Molly's mother mentioned in episodes 1 and 4 that she's 6. It's also revealed in a flashback scene in episode 10 that she graduated high school in 1991 (most people are 17 or 18 when graduating high school). If you do the math, you'll see that there's an inconsistency in her age between Seasons 1 and 2. Apparently, 2 years were added to her age in Season 2.
Character mistake: When Henry is speaking to the detective involved in investigating his father's death, the detective says that based upon evidence found at the house he requested a toxicology screen, which showed that his father died of a barbiturate overdose. He continues to explain that he found an empty bottle of hydrocodone in the bathroom trash can. Hydrocodone is an opiate, not a barbiturate. (00:07:35)
Continuity mistake: Miss Kringle's head is canted up and to the right as she lays on the gurney in the morgue refrigerator, but when Edward Nygma pulls her out, her head is facing straight up. Subsequent shots of her in the refrigerator her head is canted up and to the right.
Continuity mistake: During the street scenes it appears to be fall with leaves on the ground, grass green and streets and sidewalks dry. However, when police raid the park worker's house there is snow on the house roof and on the ground. When the police stake out the same house, there is no snow on the house roof or ground. (00:36:00 - 00:41:00)
Factual error: Sir Malcolm tells Vanessa to wear a facemask when they go to minister to the poor as cholera is rife in the area. However, the series is set in the 1890s and it had been well-known since the 1850s that cholera was caused by contaminated food and water and not by airborne germs. As an educated man, Sir Malcolm is bound to know this.
Continuity mistake: While Josh and Cooper are fighting Gabi shouts, "You need to stop fighting.., because you're bad at it and it's embarrassing," then in the next shot the top shelf of the shelving unit is collapsed with nothing on it, but two shots later that shelf is fine with the books, plant, etc, all set up properly. (00:02:45)
Factual error: In the first flashback scene of Ballard serving a Mormon mission in Lithuania, he laments that he has been on his mission for 18 months and has yet to baptize a single person. In a later flashback scene when he and his companion are visiting the prostitutes, he states that he and his companion are 19 years old and they should be in college, going to parties, getting drunk, getting laid, etc. Instead of serving missions. These scenes take place in 1991, at which time young men did not serve missions for the Mormon church until after they turned 19, so if Ballard had already been on his mission for 18 months, then he should have been at least 20 years old, and closely approaching 21.
Factual error: Henry states that the car bumper of an 2007 'XJ' is a certain height off the ground and led to a particular injury to a dead person. He claims he knows this because he is a Jaguar enthusiast. He then points to a photograph of the 'New York Kids' in a pre-2002 Jaguar XKR as 'circumstantial evidence' that it was this car that caused the injury. A Jaguar enthusiast would never mistake an XKR for an XJ.