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."
Spin Doctor - S1-E15
Continuity mistake: Nick takes to the air wearing a blue windbreaker, but lands wearing a long black duster coat. (00:14:05)
Spin Doctor - S1-E15
Factual error: Nick tells Nat about his past life as an assistant professor in the U.S., and refers to himself as "a certain indigenous vampire." Nick wasn't indigenous (native) to either the US or Canada, where the show was set. He came from Brabant, now part of Belgium. They were probably trying for "itinerant" (wandering), which would accurately describe Nick's long life.
Plot hole: Nick calls Schanke and asks him to take the Polaroids in to a lab for analysis. But Nick seems to have forgotten that he has the photos with him. They're not back at the precinct station for Schanke to take them in. (00:30:25)
Plot hole: The insertion of a musical sequence used to fill extra time in this episode creates a plot problem. It's spliced in between Nick's urgent plea for Nat to stall the autopsy and his rescuing the bound and gagged Rebecca, and unfortunately makes it appear that in that interval, Nick simply went home, played music and sat in his loft window brooding, ignoring the case altogether. (00:40:40)
Continuity mistake: Nick gets a phone call telling him another murder victim has been found and that she's been dead for at least a week. In the very next scene, Schanke says that the victim "disappeared after a date last night." (00:27:00)
Factual error: In the flashback, when Nick regenerates on the autopsy table, his shredded clothes repair themselves, too. Maybe Nick buys his outfits in the same place the Incredible Hulk does.
Plot hole: At the Precinct after the second spa incident, Captain Stonetree refers to "two unexplained reflex murders in one night." But the first victim survived the attack - so there was only one murder, not two. A little worse than a simple character mistake, since he's the police captain and knows the case. Schanke gets it right later, when he says, "One murder and one attempted murder." (00:14:20)
Plot hole: In the morgue, Nick tells Nat that vampires disappear when they die. Not so in this series. "Forever Knight's" vampires, defying old movie clichés, remained stubbornly intact when staked, making Nick's statement here a glaring contradiction of canon. (00:16:05)
Other mistake: Nick pronounces the plastic surgeon's name as "Yergen" in one scene and as "Jergen" in the next. At the end, she becomes Dr. "Yergen" again. (00:29:40 - 00:31:10)
Factual error: Nick's '62 Cadillac had an attached police radio, but never had a car phone, nor the giant external antenna attachment they required in the early 90s. Yet Schanke somehow makes a call from Nick's "car phone" in this episode.
Continuity mistake: The tow truck and the red van it's towing change positions at the alley's entrance between shots. (00:01:00 - 00:23:35)
Continuity mistake: The wooden plank with which Alexandra impales Nick completely changes angles (from flat side tilted left to flat side tilted right) between the time it strikes him and the time he pulls it out. It also appears to "grow" an inch or so wider than it was before. (00:39:00 - 00:40:25)
Factual error: The supposed ballerina in this episode's flashback to 19th century France is not employing any real ballet steps or arm movements. All she's doing on stage is standing still and waving her arms in the air, performing something that looks rather more like semaphore than ballet. (00:10:10)
Factual error: The cop who arrests Nick reads him his Miranda rights ("You have the right to remain silent," etc.) But "Forever Knight" is set in Toronto. At last report, Toronto rather resolutely insists upon remaining in the sovereign nation of Canada, where the Miranda Act, a U.S. Federal law, is not observed. (00:14:40)
Revealing mistake: The re-use of a brief scene from the pilot episode, inserted during Nick and LaCroix's vampire battle in the warehouse, creates the unfortunate problem of Nick completely changing clothes in the middle of the fight. (00:37:35)
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)
Revealing mistake: It wasn't supposed to be in shot, but the camera accidentally caught the stuffed caterpillar toy perched on Nat's desk in the coroner's lab. It was there because nursing mom Catherine Disher had her new baby nearby on set. Fans wondered, though, why the single, childless Nat would keep baby toys in the morgue. (00:17:20)
Father's Day - S2-E7
Continuity mistake: The godfather's thugs storm Nick's loft and riddle him with bullets. We actually see the bullets coming out of his back, leaving holes in the back of the vest he wears. But when the "vamped out" Nick turns around to face the camera, there are no bullet holes in the front of his vest. (00:23:20)
Father's Day - S2-E7
Continuity mistake: During his fight with Constantine's henchmen, the bullet holes in the back of Nick's vest disappear and reappear several times between shots. (00:23:30)
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.