Continuity mistake: Frazier and Marty go into the kitchen. Frazier gets out a blue bottle of water, uncaps it, puts the cap on the counter - and in the next shot we see him do the same thing again. He then goes into the living room and mistakenly tells Daphne he is going to pay for her wedding. She hugs him, and he is still holding the bottle of water. The next shot of her hugging him shows nothing in his hands, and when she lets him go, he whirls around and grabs his bottle of water off the bookcase.
Plot hole: In this show Daphne's former fiance, Clive, shows up. They had been engaged for several years in England. However, in Series 1, episode 11 (Death Becomes Him), Daphne talks about never having had a serious boyfriend, and goes into some detail about how people tried to set her up with eligible men. As Daphne is open about everything else, there seems to be no logical reason for her to not mention she'd been engaged.
Factual error: There are many factors concerning Niles' post-operative state which are very inaccurate. After open heart surgery it takes at least three months for the chest bone to heal, Niles would not be able to drive a car for weeks, nor would he be able to lift or twist which he does on the show. Also, he doesn't sport a scar. Your chest bone begins very high up, just below your neck, his scar should have been visible on numerous occasions.
Continuity mistake: At the radio station, Roz waves her pencil at Frasier through the glass to wrap up his show; she has a KACL mug in her other hand. The next shot shows her actually leaning over to pick up the mug, without enough time for her to have put it down in the first place.
Visible crew/equipment: During the closing credits, Frasier is sitting on his couch with a platter of meat beside him. Eddie is sitting up and begging for it and while he is doing this we can see the distinct shadow of his trainer's hand and arm against the couch. The hand goes higher and Eddie waves his paws higher and as the hand goes down, Eddie lowers his paws. Eddie keeps his eye on the trainer during this whole sequence. Once Frasier gives Eddie the platter of meat, the shadow disappears.
Deliberate mistake: The computer Felicity Huffman pushes off the desk is a dummy model and is not connected to anything. When she first pushes the computer off, the monitor only has a power cable visible. These computers were connected via VGA cable that was screwed on; it is quite difficult to disconnect it from the computer. And also when the monitor hits the ground, you hear light sounds of glass breaking and you can see as the monitor rolls that the glass is missing, yet none is to be seen - it's a hollow chassis. Obviously done as the stuff was shoved off in Kelsey's direction so as to avoid injury.
Continuity mistake: Frasier comes home to his apartment with a bottle of wine in a paper bag. He takes the bottle out and puts it on the table holding the bag in the other hand, but in the next shot we see the bag is already on the table and he is just placing the bottle down.
Continuity mistake: At the picnic, Bulldog puts his hand on the shoulder of a little girl in a dark pink dress, just before the pinata bashing starts; the next shot shows the same little girl is standing on the other side of the pinata, next to a woman in a blue and white striped top.
Continuity mistake: When Poppy is just about to start her show and is being emotional with everyone, Roz is standing at the door with a corded phone to her ear throughout the scene. She yells "Ten seconds." and the shot shows the phone, cord and all, has completely disappeared.
Continuity mistake: Marty and Niles are getting off the elevator and Marty transfers his mail into his left hand just as he goes to open the door to Frasier's apartment. When the shot changes to show them coming into the apartment, the mail is in Marty's right hand - there is no way he could have transferred the mail again in such a short time.
Deliberate mistake: About halfway through the show, Roz and Daphne are in the kitchen talking. Daphne pours water into the teapot - but there is no steam coming from the kettle, nor any sound of a boiling/just boiled kettle. No self-respecting Brit would make tea with water that wasn't boiling.
Revealing mistake: When Reagan drops her bag in the hallway when she is talking to Frasier, a lettuce rolls towards him. It didn't fall from her bag: if you look closely you can see it was tossed into the frame from just outside the camera view, obviously to ensure that it would land at Frasier's feet for the comic effect of him kicking it back to her.Purple_Girl