Revealing mistake: The elevator doors in Frasier's building are just a wood looking board with no safety edge sensors on the doors. These are required to detect an object between the doors. Yet, when a character touches the edge of the doors, they open back up.
Revealing mistake: The view from Frasier's apartment shows the Space Needle prominently in the background, however, the elevator that takes visitors from the ground to the observation deck is frozen in time midway to the top. This was corrected after the first season.
Revealing mistake: Towards the end of the episode, as Frasier is on the lounger by the windows, a power cord is on the ground going through the far left window (where glass should be), possibly going to the lamp.
Revealing mistake: I think there might be something wrong with the eels in this episode. They don't move in the tank, despite being alive and don't move when taken out either. Moreover, you cannot actually see any in the tank with one exception. Rubber replacements not up to standard obviously.
The Adventures of Bad Boy and Dirty Girl - S3-E7
Revealing mistake: Frasier comes in complaining how workmen in the service elevator have dribbled chili dog on his foot. He is holding out his shoe saying "How ever will I get that stain out", and Eddie runs over and starts licking what we think is the shoe. Frasier makes a comment about dog saliva being the universal solvent. In fact, Eddie does not even touch the shoe, but licks the floor in front of Frasier. Obviously the floor was treated with something Eddie would enjoy licking up.
The Show Where Diane Comes Back - S3-E14
Revealing mistake: When the waitress brings Frasier his coffee, she tilts the cup quite a lot and you can see that it's empty. (00:13:00)
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: Frasier, Roz and Ben are sitting at a table in Cafe Nervosa. However, as the camera is panning out when Ben sits down you can see the outside of Cafe Nervosa because the wall is only a small partition. The camera zoomed out too far. (00:06:30)
Roz's Turn - S4-E17
Revealing mistake: Bebe is in the booth telling Frasier how she misunderstood him about Roz. As she says "wink", we can see Frasier's reflection in the booth's glass - his head bobs up. The next shot we see, though, is of Frasier's head bobbing up - shot at the same time, we just see it a split second later.
Revealing mistake: At the end of the episode when Frasier reveals to everyone that Roz is the one who's pregnant, we see Peri Gilpin step into the shot at the top of the stairs too early. She steps back behind the wall and then walks back out again a second later to say her line.
The Show Where Woody Shows Up - S6-E13
Revealing mistake: Frasier and Woody look at the Seattle tourism book, and in particular a photo of the city. However, you can see there may be some text on the page, but there certainly isn't a photo.
Revealing mistake: After Donny puts the phone onto speaker you can see him deliberately wiping the mustard from the sandwich across his left cheek to prepare for the gag at the end of the scene. (00:06:45)
Revealing mistake: In the scene where Frasier and Lilith meet in the living room, where Frederick has created a romantic atmosphere, Frasier has a long speech about how Lilith is not going to get him back, ending with "I need to be finessed!" and Bebe Neuwirth goes out of character and begins to giggle, before she quickly covers her mouth and pulls herself together. Though Lilith might have found Frasier's comment amusing, it would definitely not be in character for her to giggle like that.
To Thine Old Self Be True - S7-E20
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.
Revealing mistake: After Niles tells in front of everyone at the party that he loves Daphne, you see Frasier in one shot standing near the guests by the front door. You can see the set wall ends above the fireplace and a black wall is behind it.
The First Temptation of Daphne - S9-E3
Revealing mistake: Frasier and Martin are arguing in the kitchen about the cricket. Martin opens the fridge to grab a beer and slightly bumps the fixed island in the kitchen, which moves.
Revealing mistake: It's clear the "Manchester" pub scene was filmed in the United States, as the pint glasses used are American pints and not imperial pints as used in the UK, which are approximately 20% bigger.
Revealing mistake: When Frasier drives into and breaks the barrier at the parking garage, you can see that the barrier snaps very cleanly at an obviously pre-cut point.
Revealing mistake: When Frasier and his guest are standing up to leave, the girl behind the counter is watching them for her cue to come over.
Revealing mistake: Even though she has customers in front of her, the barista can be seen watching Frasier and his guest as they are talking, so she can see her cue to come over.
Answer: In the last episode, they explained that Tossed Salad and Scrambled Eggs is a metaphor for the mixed-up people to whom Frasier dispenses his radio psychiatric advice.