A Man, a Plan and a Gal: Julia - S11-E2
Continuity mistake: As Frasier is protesting his love for Julia and says "the essence of music", Daphne's hands go from being on the couch to being folded on her knees, without enough time to do it in real time.
Continuity mistake: When Martin and Frasier are in Cafe Nervosa and Marty is lecturing his son about eavesdropping, his newspaper moves a few inches, from being on his left to being right in front of him, even though he never touched it.
Boo! (a.k.a. I'm With Her) - S11-E16
Continuity mistake: Marty is home from the hospital and there is a basket of flowers on the coffee table. The basket moves several inches to the left while Niles goes to the door to let Ronee in.
Continuity mistake: After Frasier watches the video of Eddie, he tosses the remote on the coffee table. When Niles comes in a short time later, the remote has disappeared, but when Niles asks, "Aren't you going to ask me what's up?" we can see the remote again, on top of the manila envelope. It disappears and reappears throughout the scene.
Continuity mistake: During the opening credits, Roz and Ann are sitting in Cafe Nervosa - just before Roz says "Frazier" we see Ann put her mug down. When Frasier approaches, we see her put it down again.
Continuity mistake: When Roz is talking to Martin in the cafe, she takes a cookie from the plate, but in the next shot she gives the brownie to Martin with the same hand and the cookie is nowhere to be seen.
The Ann Who Came to Dinner - S11-E13
Continuity mistake: Maris is hiding in a wooden box so she will be shipped out of the country. Marta, her housekeeper, has a protein shake for her, and puts the straw through a hole in the box. Maris indicates that she's drunk too much and Marta goes to put the straw back in the hole so she can regurgitate some - but just before that happens we see a stream of the liquid come out of the hole and dribble down the box. In the next shot the straw goes into the hole and the box is all clean and dry again.
Continuity mistake: Daphne comes into the Cafe and asks Marty, "Where have you been?" and her purse is on her right shoulder. In the next shot her purse is in her hand, but not enough time had passed for this to happen naturally.
Continuity mistake: At the end of 3-10 in the airport with Kate, Frasier says that he has an allergic reaction to cats but here he cat sits for Mr. Bottomsly.
Suggested correction: This has been addressed in the Questions section. Frasier is apparently choosing to deal with his allergies, in order help the cat's owner. It's also possible for allergies to be triggered by one cat, but not another. It depends on the amount of dander that the particular cat produces, and the level of Fel D. 1, a protein in their saliva.
Continuity mistake: When Niles and Frasier are in the cafe discussing how many patients have fallen in love with them, Frasier claims 13. But in the episode "The Maris Counsellor," he states no patient has ever fallen in love with him. OK, time has passed, but he's done hardly any private practice since then, and any he did do was shown anyway.
Boo! (a.k.a. I'm With Her) - S11-E16
Continuity mistake: In the first scene after Niles walks in and takes his coat off. The left-hand side of his shirt collar alternates between tucked underneath his jacket and sitting outside it.
Goodnight, Seattle (2) - S11-E24
Continuity mistake: When Eddie eats the wedding ring at Martin's wedding, there's no food on his plate, next shot there is.
A Man, a Plan and a Gal: Julia - S11-E2
Continuity mistake: When Frasier is playing pictionary, his drawing of Jerry Garcia changes noticeably within shots without him touching it.
Continuity mistake: After Gil comes into Frasier's booth to talk following the 'outing' caller, Frasier begins packing his briefcase, then shuts it. Seconds later, it is still open and he shuts it again.
Match Game - S11-E18
Continuity mistake: The scene where Charlotte comes to Frasier in the restaurant to tell Frasier his date has cancelled is poorly edited between shots. Watch the folder once she has pulled it out: in almost every shot, the side facing the camera changes, and when Charlotte gets up, it disappears completely.