Revealing mistake: About 1/3 through the episode, they are in Roz's apartment. If you watch when people enter or leave the apartment, the door has a handle lockset. It also has a lock cylinder about 1 1/2 feet above it on both sides of the door. The problem is, the side of the door has no drill hole where the latch assembly should be: it's just solid wood. The lock isn't attached to anything that would enable it to work.
Revealing mistake: The guy who plays Clive in this episode has one of the most appalling accents I have heard. He's apparently from Manchester, but sounds like a sort of cockney South African. His accent slips around all the time; it's very poor. I wouldn't normally submit it, but his is so shockingly bad I doubt anyone would be fooled into thinking he was British.
Continuity mistake: During the opening credits, Frasier is playing the piano and Martin is going through papers on the table. When Marty says "I don't know, Eddie, must you?" there is something pink lying on the table. The shot goes back to Eddie and then back to the table, but the pink item has disappeared.
Continuity mistake: There was an episode in which Martin attempts to end a feud between Frasier and Niles by telling a story about his detective partner. He starts with the line, "I never had a brother...", but in the episode about Frasier's cousin Nikos getting married, Martin's brother Walt was introduced.
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.
Continuity mistake: Frasier (and later the others) come back to his apartment to avoid the rain - they shake off umbrellas, and we even hear the storm at the very start of the scene. However there's no rain on the balcony - can't be covered, as we see in "Call Me Irresponsible" during the obligatory sex scene that when it's raining the balcony gets soaked.
Continuity mistake: During the first episode of Frasier there is a painting of some vases in Frasier's apartment which is at the end of the hall leading on to Daphne's Room. In this episode the painting has a red and purple background, however in 'Here's Looking at You' (S1, 2 mins 52 secs) the exact same painting is now red and blue. It remains this new colour for the entire 11 seasons. (00:06:50)