Fool Me Once, Shame on You, Fool Me Twice... - S2-E14
Continuity mistake: Daphne is visiting KACL and has Frasier's headset up to her ear and then down on the console in a split second, with not enough time to do this naturally. (00:13:45)
Continuity mistake: At the start of the show Niles is playing the piano. He turns to talk to Frasier and his hands are in his lap, but in the next shot one hand is back up on the piano keys, with no time for this to have happened naturally.
Revealing mistake: The elevator doors in Frasier's building are just a wood looking board with no safety edge sensors on the doors. These are required to detect an object between the doors. Yet, when a character touches the edge of the doors, they open back up.
Forgotten But Not Gone - S8-E18
Continuity mistake: While Marty and Frasier are eating Fredericka's cooking, Frasier puts his knife down on his right, then switches his fork to his right hand. After he says "motion carried," the shot shows his fork back in his left hand.
Frasier Crane's Day Off - S1-E23
Continuity mistake: Martin and Frasier are having breakfast and Marty is making fun of Frasier's radio audience. In one shot Marty's arms are folding on the table in front of him over his newspaper - in the next shot one arm is stretched out over the newspaper and the other is at 45 degrees angle in front of him.
Guess Who's Coming to Breakfast - S1-E13
Continuity mistake: Marty, Elaine, and Frasier are sitting down to breakfast. Elaine picks up her mug and in the next shot we see her reach and pick it up again.
Continuity mistake: While Frasier and Niles are having coffee outside at Cafe Nervosa, a red napkin is by Frasier's cuff. In the next shot it is suddenly in the center of the table, even though no one touched it.
Roz's Krantz & Gouldenstein are Dead - S4-E15
Continuity mistake: Frasier is on the couch talking to Niles. As he says "I simply release my humble words", his hand switches from being around the middle of his bottle of water to being around the neck, with no time for natural change.
Continuity mistake: Daphne comes into the Cafe and asks Marty, "Where have you been?" and her purse is on her right shoulder. In the next shot her purse is in her hand, but not enough time had passed for this to happen naturally.
Roz's Turn - S4-E17
Continuity mistake: When Frasier, Roz and Bebe are arguing, Frasier says something like "she has no reflection." When he says this you can just see Bebe's hands in the shot and they are clasped together. In the next shot they are instantly quite far apart.
Continuity mistake: At the end of 3-10 in the airport with Kate, Frasier says that he has an allergic reaction to cats but here he cat sits for Mr. Bottomsly.
Suggested correction: This has been addressed in the Questions section. Frasier is apparently choosing to deal with his allergies, in order help the cat's owner. It's also possible for allergies to be triggered by one cat, but not another. It depends on the amount of dander that the particular cat produces, and the level of Fel D. 1, a protein in their saliva.
Guess Who's Coming to Breakfast - S1-E13
Character mistake: In this episode Roz comments that Noel drives a 1973 Dodge Polaris. There is no Dodge Polaris. There is, however, a Dodge Polara.
Liar! Liar! - S4-E10
Continuity mistake: At the beginning of the show, we see Marty add some beer to his champagne glass until it's almost full - just then Bulldog grabs his SeaBee award from the coffee table and now Martin's glass is almost empty, even though he's had no chance to even take a drink.
Continuity mistake: Kelly comes over to Frasier's to read a mock script for the Xmas parade Frasier wants to co-host. She puts her purse next to her on the couch but never opens it. Suddenly reading glasses appear next to the purse, which Kelly subsequently puts on to read.
Character mistake: Frasier tells Niles that the article on him will be in the winter/spring issue of Seattle Broadcaster. The man who interviews him introduces himself as a journalist from the Seattle Times.
Continuity mistake: In the episode "Call Me Irresponsible" from season 1, Frasier and Catherine are making out on Martin's old chair, which starts vibrating (probably because they inadvertently hit a switch on the side). But in "Give Him the Chair", Frasier tries to replace Martin's old chair by buying a new one which has a built-in massager. When Martin tries it, he looks horrified and says "That's disgusting", even though his beloved chair had the same feature.
Plot hole: When Frasier is trying to get to the bottom of Niles' problem viewing Daphne in a real way, we see them both against past scenes in the show; Frasier watches and comments on some of them as he talks but because he is actually only discussing these events with Niles, he shouldn't be able to see a visual of anything such as the dress Daphne is wearing during the dance scene.
Continuity mistake: When Niles and Frasier are in the cafe discussing how many patients have fallen in love with them, Frasier claims 13. But in the episode "The Maris Counsellor," he states no patient has ever fallen in love with him. OK, time has passed, but he's done hardly any private practice since then, and any he did do was shown anyway.
Something Borrowed, Someone Blue (1) - S7-E23
Visible crew/equipment: As Roz and Simon are leaving, and Niles enters the apartment just before telling Martin he's married, the camera pans far too wide. On the left-hand side of the screen, you can easily see the end of the set and crew members in jeans standing around.