When Daphne (Jane Leeves) is speaking to Niles (David Hyde Pierce) during the party, she reaches to her right eye with a tissue. However, when the camera changes, she is reaching for her left eye.
During the back and forth dialogue between Fraiser, Niles, and Daphne at the end of the episode, the tail of Fraiser's hat switches positions multiple times.
As a drunken Niles argues with Frasier, the level of his drink repeatedly rises and falls.
When Niles and Frasier are arguing and Frasier thinks he's talking about Roz, Frasier says, I suppose I can give her a raise! But it's been said in multiple episodes,that Frasier does not pay Roz's salary. The radio station does.
At the party, when Niles and Frasier are arguing and while Frasier is about to let the cat out of the bag about Roz, you can see Peri Gilpin at the top of the stairs pop out from behind a wall, quickly go back, then turn around and re-enter the scene, obviously mistiming her cue.