In the restaurant Frasier says "There's an ocean of fresh fish not 15 feet away," and you can even see the blue reflection of the water and it's movement as it laps against the shore. Why then, can't you hear waves crashing at all? This is especially strange as in every other scene in this restaurant you can hear it, but not in this particular one.
In the previous episode, Roz said she wanted "Friday the 15th" off. The only Friday the 15th in 2001 was in June, so presumably, this episode, set in May, takes place before the end scene of the previous episode, which takes place a few days before June 15th!
When Frasier is talking with Claire in the electronics store amidst the DVD organizers, a wedding band on his left hand disappears and reappears several times in between shots.
Daphne refers to "a youthful indiscretion" wherein she stole a teddy bear from the shops. By the time her story is done, she comes off sounding more like a saint than a sinner. In Season Eleven's "High Holidays", however, we get an entirely different picture. She says that as a teenager she was into (among other things) shoplifting - to the extent that she can carry a frozen turkey between her knees.
When Frasier mentions him, Claire says that she loves Kierkegaard. Søren Aabye Kierkegaard was a 19th century Danish philosopher and theologian, generally recognized as the first existentialist philosopher.
Frasier did not speak German as of "An Affair to Forget".
Perhaps he has learned since then, or that earlier episode was simply
inconsistent – since it is virtually required that any serious student
of Freud should read him in the original German.
Niles and Daphne have consulted a professional to determine if Daphne is, in fact, psychic. As an audience, however, we have ample evidence that she is. On first meeting Martin, she knew he'd been a policeman; she sensed that Frasier's gay boss had had a dispute with a former lover over opera records which caused him to suddenly sit down in shock (even Frasier witnessed that). She also had a vision of her "true love" (Niles) with a dragon, and as we saw, he had been given a dragon figure by Roz. Many other visions (usually comic) also support her claim.
The first symbol card we see Dr. Morey show Daphne she says is a star. As he lays the card down you can see that it is two wavy lines.
When Frasier is standing at Roz's door, there's a picture of a woman visible just below the light switches. The woman resembles Peri Gilpin a great deal and may very well be a picture of Peri's real life mother. Of course, in the context of Frasier, her mother is played by Eva Marie Saint, but perhaps the picture was put there for Peri's sake - to be thought of as Roz's aunt or other relative.
The vegetable chopping was either refilmed at a better angle to insert season 8 Frasier and Niles or it was a different take from the one aired in "First Date". The most obvious difference is that Niles' voice overwhelms Daphne's when they sing together, whereas Daphne's is dominant in "First Date". Also, Daphne stops chopping too early on.
Martin: (Exit line to Frasier and Niles at the wine club) Now, if you don't mind, I've got a big plate of Gewurzplatzchen waiting for me at home with my name on it.
Gewurzplatzchen are German spice cookies.
Goof: In one scene one of the servers at Frasier and Niles's wine party trips and sprains her ankle, and is helped to a seat to sit down. However, in the next scene of Frasier and Niles talking in the kitchen, she can clearly be seen in the background serving people.
(Frasier has just handed Martin 4 Sonics tickets)
Martin: Looks like I owe you an apology.
Frasier: An apology?
Martin: Well, last October you said we would go to a game together, but I thought that was just a lot of talk.
This refers to the October episode, "The Bad Son", in which Frasier, in telling Martin he doesn't want him to move to the retirement home, says that he wants them to do more things together, including going to Sonics games.
The music that is playing while Niles is attempting his half-court shot is "Sirius" by The Alan Parsons Project.
Frasier: (to Martin) At this precise moment, she (Monica) should be receiving a Jeroboam of chilled champagne.
A Jeroboam is a 3-litre bottle of champagne, twice the size of a Magnum. The largest bottle of champagne is a Nebuchadnezzar at 15 litres.
In the middle of the episode, while siting in Cafe Nervosa with Roz, Kelsey Grammer accidentally calls her "Niles."
Kelsey Grammer had appeared in an episode of Star Trek: The Next Generation as Captain Bateson in the episode "Cause and Effect." Both shows were produced by Paramount Pictures.
Frasier is sent to a Sci-Fi/Comic convention in search of an X-Men comic book for his son. Eventually Kelsey Grammer would go on to play "Beast" in X-Men: The Last Stand.
This is the only episode in which Martin was ever in Roz's apartment.
Frederick is 13 in this episode, which aired in January 2001. But on "Cheers", he was born in November 1989, so he should only be 11 years and a couple of months old!
Additionally, in "Star Mitzvah" in Season 10, Frederick is just turning 13, and having his bar mitzvah.