During the scene where Fran is chatting with Steve and Eydie, as the camera angles change, the passersby appear and disappear depending upon the angle (particularly an elderly lady).
Fran alludes to cannibalism and the infamous Andes flight disaster, rejecting Sylvia's assertion that she'd eat Fran last with "Not if I was the only kosher corpse!" A kosher human corpse is a logical impossibly, as halakha enjoins Jews from the eating of human flesh, and humans would not meet the criteria for kosher animals even if it wasn't specifically prohibited.
When Niles is dancing in the foyer, the outline of white briefs can be seen underneath his boxer shorts. Actors who usually wear briefs frequently wear boxers in underwear scenes to appease network censors.