Factual error: Nick tells fellow vampire Aristotle, "You still owe me for that time at the Battle of Hastings." Nick was brought across in 1228, or so the intro told us every week. The Battle of Hastings, as any British school kid knows, was fought in 1066, over 100 years before Nick's mortal birth. (00:29:30)
Continuity mistake: The blood stains on Nick's white turtleneck are lighter, then darker, then lighter again, and migrate to different positions, both during his fight with LaCroix in the abattoir, and throughout the hospital scenes afterward. (00:10:15 - 00:19:30)
Plot hole: Nat thinks Nick is becoming more human because he can see himself in the mirror, and he replies, "Only sometimes." This line contradicts series canon, as "Forever Knight" did not adhere to the vampires-don't-appear-in-mirrors cliché. Nick was seen to reflect very nicely, in fact, every time he passed a mirror, and not just "sometimes."
Plot hole: Near the end, a cop comes to tell Schanke that an explosion has been reported at Nick's place. But neither of the two intruders uses any explosives. One shoots his way in through a door and the other breaks in through a skylight. Neither makes enough noise for the disturbance to be called an explosion. (00:41:15)
Factual error: As the creepy "Nightcrawler," master vampire LaCroix taunts Nick via his CERK radio broadcasts, which Nick listens to on his Cadillac's car radio. Except, CERK's studio sign says it's an FM station. And Nick's Caddy, supposedly a '62, still has its factory radio (we get lots of good close-ups of that), which in 1962 was strictly AM. So how was he receiving LaCroix's station?
Factual error: Though she wore medical smocks and occasionally a baseball cap to hold back her hair, Natalie was never correctly attired when she performed her autopsies. In fact, she usually worked with her hair loose and hanging down over the corpse, which may have made her look prettier, but is a serious breach of forensic etiquette that could contaminate the evidence. Even the best-coiffed coroners still have to wear sterile caps and gear.
Continuity mistake: Schanke calls Nick to tell him they've found Mrs. Hedges' body, and says, "They cut her throat, man." We even see a brief shot of the bloodied corpse. But later in the morgue, Nick says, "She was asphyxiated, right?" and Nat agrees. The corpse on the autopsy table now appears to have an intact throat. So, which way did Mrs. Hedges die? (00:22:15 - 00:38:10)
Revealing mistake: The flashbacks to 1228 in this episode portray some of the same events - Janette seducing Nick, LaCroix making Nick a vampire - that are also shown in "Dark Knight." But here, Nick, Janette and LaCroix are all wearing completely different costumes.
Factual error: The murder victims, all Catholic, are specifically said to have "all worn crucifixes." But the jewelry Nat hands Nick as evidence, the cross that burns his hand and the necklace Magda later gives him are all plain crosses, not crucifixes. (The former is unadorned; the latter has a Christ figure on it.)
Revealing mistake: When Schanke, in a huff, packs up his treasures and moves out of Nick's loft, he kicks the box of his belongings into the freight elevator, then gets in and closes the door. If you watch closely, you can see the cord of his duck lamp caught under the door, where it stays even after the elevator supposedly begins its descent. (00:31:55 - 00:34:55)