Deliberate mistake: The background of the street scene from Frasier's apartment balcony shows cars and other vehicles but they are always standing still.
Continuity mistake: Frasier is based on the character originally created on Cheers. In Fraiser, he lives with his father who is a retired police man. On Cheers, Frasier once mentioned his father was a scientist. It's also worth noting that in one episode of Cheers, John Mahoney, who was to later play Frasier's dad, turns up as a pianist. Frasier also said on Cheers that his father was dead. When Ted Danson made a guest appearance on Frasier, Frasier admitted that he had lied about his father since the two had been arguing so much.
Continuity mistake: Across the show, Marty is supposed to be about 21 years older than Frasier (he turns 65 in season 5). There are at least two problems with his age - Frasier is supposed to have been born in March 1952 and in Season 5 (Roz and the Schnoz) Marty mentions going on shore leave as a single guy in 1952. Even if he was confused about the year, Frasier didn't call him on it. He must have done just a short stint in Korea as he was already a cop when he met Frasier's mother - they met at a murder scene, and he must have been 20 years old at the most. She was already a full fledged psychiatrist.
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.
Answer: Nanny G (Nanette Guzman - played by Laurie Metcaf) has been a children's entertainer for twenty years, and tells Frasier, "Do you know what it's like to play the same character for 20 years?!" The joke is that Kelsey Grammer has been playing Frasier Crane since 1984, when the character first appeared on "Cheers", so Kelsey in real life has been doing just that!
Super Grover ★