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.
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 ★