During the first scene at Cafe Nervosa, Roz's cup fluctuates between frothy and no froth.
Despite an official "Klingon Dictionary" being available since 1985 (13 years earlier; revised 1992, 6 years earlier), the writers did not use an official translation such as "DaH jImej" for the word "goodbye". Instead, Noel (Patrick Kerr) gives Frasier (Kelsey Grammer) a seemingly random phrase, "krish-krush", which is meaningless in Klingon.
When Frasier is writing his check out to Roz, at the bottom of the check he signs the left side and puts a straight line through the right side (the memo section). Normally the signature section of a check is on the right side and the memo on the left.