Continuity mistake: During the opening credits, Bulldog is on the phonein the hall at KACL and he throws a tennis ball at Frasier, who stumbles around trying to catch it. During the scene we see an extra behind Bulldog go into one of the rooms - but we see her do it again just a split second later - and the second time she has a paper under her arm, where she had nothing the first time.
Continuity mistake: When Roz and Frasier are in Bebe's office, and Frasier is exclaiming about her taking digitalis, the water glass in front of her is empty. The rest of the shots show it being about half full, even though she never refilled it, and there was no water source to be seen.
Continuity mistake: At the beginning of the show, when Niles and Frasier are in Cafe Nervosa, the man behind them has a paperback book which is open with all the pages fanned out, and then it is lying flat, then fanned out again, and so on. It is not a case of him changing the book naturally, as the positions of other things in the shots change slightly as well.
Continuity mistake: Frasier and Daphne are on the elevator; Daphne has a bag of groceries. In some shots several inches of a loaf of French bread is seen, but when she gets off the elevator the bag is sealed up with no bread visible. The bread becomes visible again in later shots as they talk at the door and go into the apartment.