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: When Bulldog gets back to the kitchen table after closing the door on Roz's date Ted, there is a large blue casserole dish sitting there - it wasn't there when he went to answer the door. Roz had been hiding the whole time, so she didn't put it there.
Continuity mistake: Roz is at Daphne's shower, saying "God, he sounds just like a prince," in reference to Simon - in her left hand is a drink and her right hand is positioned down, as though it is in her pocket. In the next shot she is still holding her drink in her left hand, but is giving Daphne a drink with her right hand - it just appears out of nowhere.
Continuity mistake: Frasier is just saying goodbye to Niles and we can see the brochure for Daphne's reception to the left of his sherry glass. When he stands up and shouts "Daphne!" the brochure has moved about 6 inches to the right, even though no one touched it.
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.
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.