Continuity mistake: At the beginning of the show, Frasier gives Roz an evening purse in a box. She puts it back in the box and as they talk we can see the edge of the box - from one shot to the next we can sometimes see the strap hanging out and sometimes not. The camera angle does not change.
Continuity mistake: Early in the show, at Cafe Nervosa, Roz comes in and Bebe asks her to get her some coffee. Roz returns with a paper bag which she puts down on Bebe's right. In the next shot Bebe stands up with it in her left hand, but there was not enough time for it to change from the right to the left naturally.
Continuity mistake: During the part of the show where they are getting ready to play Murder we can see empty punch glasses on the table - in another shot we see three even though no one went near them. This changes back to 2 after the lights come on - unlikely anyone helped themselves to punch when the lights were out.
Continuity mistake: If you look closely at the couch in the first scene ("A Valentine for Niles") it is not the same couch used during the rest of the run of Frasier - it looks brand new and it doesn't quite have the same texture or look. It makes sense, as Niles sets fire to the couch at the end of the scene.
Continuity mistake: Frasier and Marty are sitting in their living room talking about Frasier's problems with women. Marty has his fork poised above a plate with a slice of cake on it. The next shot shows the fork on the plate, next to the cake. Marty would not have had time to put the fork down in the split-second in between.
Continuity mistake: Frasier is in the kitchen and gets the sugar out to sprinkle over the profiteroles. As he starts shaking we get a wider shot and we see there is sugar all over the stove top, pastries, plate, and counter - way more than there should be for the amount of shaking going on.
Continuity mistake: Fairly early in the show Frasier has his dad call the police station to ask about a female officer Frasier is interested in. Marty asks for her name, hangs up, and gives Frasier a lot of information about Maureen that he couldn't have possibly learned in that short a time.
Other mistake: In the kitchen, when Niles burns his hand you can see him move his hand down to stop the frying pan from falling off the stove. He doesn't touch it again, but it looks like the instinctive actions of someone who knocked something over rather than part of the scene. He just slips out of character for a moment.David Mercier
Continuity mistake: About two thirds of the way through the show, Marty and Frasier are talking in the living room. Marty is sitting in his chair with a glass of milk. One shot shows him with both hands on his milk, and then he puts his left hand on the arm of the chair. In the next shot his hands are around his glass of milk again.
Continuity mistake: Niles runs into the kitchen where he finds Frasier cleaning the oven. As Frasier stands up, one of the cuffs on his rubber gloves has been turned over, and the other hasn't. A couple of shots later they are both neatly folded over. As Frasier leaves the kitchen, they are back to the first position. At no time did he adjust them.
Continuity mistake: Marty and Sherry are looking at old photos to use at Marty's birthday party - we can see one in Sherry's hand that has noticeable brown marks down the back, as though it had been glued in an album. The next shot shows Marty passing this one to her, even though in the shot before it was in her hand. When Sherry passes the picture over to Niles and Frasier, in the shot when they get it, it's not the same photo, as it is clean on the back.
Continuity mistake: In Cafe Nervosa, after Niles has taken off all his clothes, Frasier wraps him up in a couple of Cafe Nervosa aprons and Roz picks up Niles' clothes from the floor. In one shot, we see his tie towards the top of the pile in Roz' arms, and in another it is swinging free at the bottom of the pile. The clothes change position in her arms from shot to shot. In one shot the boxers are still on the table, with a newspaper. In a subsequent shot, Roz has the boxers. When Niles is being taken outside, the table nearest the door has only a cup on it. In the next shot, we see the newspaper on the table again.