While Frasier, Niles, and Martin are toasting their troubled love lives, after three toasts Niles over fills Martins glass, but while they are talking it can be noted that at first the glass is full, then for a short period it's only half full, then just as they complete the toast and drink their drinks the level is back up again.
While Niles and Frasier are discussing the possibility of Maris's love for Schenkman being transference, Frasier states that he hasn't had any patient fall in love with him. On Cheers (1982), Diane Chambers was Frasier's patient, and she fell in love with him.
Roz puts through "Roger on line two", but Roger never actually gave Roz his name.