Continuity mistake: When Niles and Kit are at Frasier's apartment, Kit does a quick dance with her arms out and tells them Niles is taking her to Euro Disney. A couple of shots later her little purse is back under her arm, even though she had no time to pick it up from the bookcase.
Continuity mistake: Frederick appears in the kitchen to talk to his parents, who are ignoring him. In one shot he is covered with spots and in the next, he only has about half as many. He is supposed to have hives, which I know can appear and disappear quickly, but these look nothing like hives in the first place.
Continuity mistake: When Frasier and Kate are in the airport, sitting down and talking, her arms switch back and forth from being folded to unfolded (holding her boarding pass). This happens a couple of times, without time for her to change position.
Continuity mistake: There are several bad cuts between shots when Niles and Frasier are on the balcony. Keep an eye on the height of Niles' sherry glass. The most noticeable occurrence is when Niles mentions "detachment" and the shot changes. He is suddenly holding his glass at least a foot higher in the air.David Mercier
Continuity mistake: When Frasier, Marty, and Niles are having drinks at the end of the show, Frasier says "I think we have a 3-way tie" and we see Marty holding his drink in his left hand - the shot then switches and it's suddenly in his right hand, with no time for a natural change.
Continuity mistake: When Frasier is in the boardroom with Roz and her production team, Frasier is writing in a binder, which is on top of a couple of books. In some shots we see a couple of different books in front of him on the table. One of them is called "Mars," which he had put back in his briefcase at the beginning of the scene.
Continuity mistake: When Daphne is playing darts with Frasier, he says, "I scored again," and we see her sweater sleeve is pushed up her arm. But when she comes back with, "That's not something we hear very often," the sleeve is completely covering her arm. In the next shot, it's pushed up her arm again. There was no time for the adjustment.
Continuity mistake: Niles and Frasier are at Marty's old apartment and Niles sits down on the couch. Eddie is sitting next to him, staring. During this scene, the shots of Eddie show him moving from fairly close to Niles, to about 10 inches away, and then back again. He has no time to change position naturally.
Continuity mistake: Frasier, Martin, Niles, Daphne, and Diane are having dinner at Frasier's and he gets up to get dessert. Niles offers to help him and puts his table napkin in his chair. As he walks towards the kitchen, though, the napkin is lying next to his plate.
Revealing mistake: Near the end, in Cafe Nervosa, the guy that wants to sue Frasier gives Niles a push. Niles stumbles backwards, knocking over some chairs and the coat rack before falling down, taking the table by the window with him. If you look closely just before he hits the table, the woman sitting there (rather than moving out of the way), very subtly pulls on the table, so as to upend it so Niles can go down with it.
Revealing mistake: At Cafe Nervosa, after Niles has had a mini-breakdown, he has shed his clothes, boxers and all, all over the place and is supposedly naked in the corner with only a newspaper for privacy. When Frasier has him stand up to wrap aprons around him, one can see that David Hyde Pierce is actually wearing light-coloured briefs.