(Episode references in parentheses.)
Marty plays chess and knows the names of chess pieces (1.14) but needs to be taught how to play chess and to learn the names of chess pieces. (3.18)
Niles claims his regular drink is a latte with nutmeg and cinnamon (1.22) but he can't have nutmeg because it inflames his stomach lining. (5.8)
Marty has never had a brother (1.22) but is reunited with his brother Walt at a wedding. (5.16)
Niles says his housekeeper Marta is 78 years old (1.23) but she is clearly much younger. (2.21)
Frasier and Niles high-five each other easily, vigorously and often (1.24, 4.12 and 5.18) but Niles is clearly unfamiliar with high fiving altogether (3.2, 7.16 and 6.6).
Duke tells Frasier that Marty told him when Frasier's wife was "screwin' around behind [his] back" (2.5) but Marty never knew anything about it. (1.8)
To Roz's sister Denise, Frasier is introduced as "Roger" (9.23) but she later interacts with him as Frasier. (11.10)
Marty calls his political commercial for Holden Thorpe a "spot" (2.7) but he doesn't know what that term means. (11.11)
Daphne tells Bulldog the shower is down the hall, second door on the left (1.10), but there are no doors on the left. (3.18 and see the floorplan of the apartment here)
Maris sleeps with a pearl-handled revolver under her pillow (2.10) but she doesn't have a gun in the house. (3.1)
Marty never took any home movies (2.11) but took quite a lot of home movies. (7.1)
Niles had a girlfriend in his senior year of college (11.8) but he's never dated anyone other than Maris and his pen pal from Costa Rica. (3.13)
Niles learned at his first wedding that he's plagued by a congenital heart murmur (2.16) but he has no idea that he has any heart condition. (10.7)
Daphne has never had a serious boyfriend, (1.11) but was engaged to Clive Roddy in 1991, two years before coming to Seattle (4.1) and her boyfriend before then proposed to her too. (6.22)
Niles eagerly and immediately picks up Frasier's Wassily chair to move it (1.1) but he never lifts furniture. (3.5)
Frasier has an aversion to social hugging (4.22) but comfortably hugs others socially all the time (2.16, 1.12, 1.22, 5.13, 6.13) and sometimes has overwhelming urges to hug others. (1.1)
Frasier's Study is right across the hall from Marty's bedroom (1.1) but is on the far side of the apartment, (2.17 and 3.12) forty-one steps away from Frasier's bedroom, (2.18) and there are no rooms across the hall from Marty's bedroom (see apartment floorplan at the bottom of the Home page).
Frasier does theme-based shows on the air (1.2, 8.4, 10.5 and 3.11) but refuses to do theme-based shows. (3.1)
Marty insists on saying a prayer before meals (1.4) but never does again.
Niles and Maris sleep in separate rooms (1.9 and 11.8) but sleep in the same bed. (5.13)
Niles became wine club president after Brewster Cale resigned following a prank Niles played on him, (1.5) but he has never been the wine club president despite always wanting to be. (7.17)
From the kitchen Daphne easily overhears a conversation in the living room, (1.5) but it's assumed in all other episodes that it's not possible to overhear conversations between the kitchen and the living room.
When violating his ethics, Frasier becomes nauseous and physically sick (1.7) but with Dr. Honey Snow and while reading T. H. Houghton's manuscript he violates his ethics without any physical side effects. (2.15, 4.4, 11.15, 11.17 and others)
Bulldog bites a pickle offered to him by Marty but the remainder of the pickle is larger than it was after the bite. (1.10)
Lake Chelan is not pronounced by locals "Lake Shalonne" (1.11)
Marty has always hung the same Christmas wreath since 1967 (1.12) but in subsequent years it's a completely different wreath that he's always hung. (3.9)
It's not in Niles's nature to cry (1.17) but he cries easily (3.14, 6.3, 9.15 and 5.6) especially when others are crying. (4.8)
Maris's quadriceps are too tight to straddle anything larger than a border collie (2.21) but Niles buys her a most exquisite antique saddle (5.10) and she straddles a frozen butterball turkey.
During a blackout, Martin says that the power is out all over South Seattle (2.24) but the power in their North Seattle apartment is out, and the whole of central/downtown Seattle is visibly dark instead.
The wine club leader's title keeps changing from President (1.5) to Maître d'Chai (3.5) to Corkmaster. (7.17)
Frasier is highly allergic to cats (3.10) but can keep a cat in his apartment without any allergic reactions. (11.5)
Niles is an accomplished "kitchen person" (1.13) but needs to learn how to cook. (3.10)
Niles and Maris honeymooned in Zurich (1.17) but honeymooned in Vienna (3.8) even though they honeymooned in Gstaad (11.8)
Niles' housekeeper Marta speaks no English (2.21) but speaks English fluently. (3.8)
The version of "Buttons and Bows" sung on television by Frasier is different than the recording of it watched by Marty and Daphne. (3.16)
Cast member extras repeatedly show up in different venues. For example, the same cast member extra sitting next to Roz taking calls during the PBS pledge drive (3.16) is frequently seen at Café Nervosa. (3.18) A cast member extra sitting behind Daphne, Niles and Marty at a basketball game (4.5) is a boisterous fan sitting next to Niles at another basketball game. (8.15) Actor Griffin Dunne plays Russell in one episode (1.1) and Bob in another. (3.11)
Niles cannot ride a bike, skip a rope or kick a ball (3.13) but can play tennis (3.15) and squash (4.10) and Tai Chi (9.1 and 2.4) and kickboxing. (7.16)
Le Cigare Volant has a jackets-required dress code (1.3) but jackets are not required. (4.9)
Frasier doesn't know where a screwdriver is (4.11) but knows exactly where his Hammacher Schlemmer tool-set with a screwdriver is. (2.11)
Marty's birthday is shortly after Thanksgiving (4.9) but Marty's birthday is late in Spring (2.24) and yet he's a Libra - born between September 24 to October 23. (5.19)
Niles never flew coach class before (3.22) but has flown coach class before. (4.24)
Frasier's headphones fall forward over the front of his radio studio desk (3.24) but there is a wall immediately in front of his radio studio desk. (1.12)
The apartment complex shown bears little resemblance to Frasier's apartment complex (Elliott Bay Towers) - notice for example, the shape of the balcony - and Frasier's bedroom light should be the floor immediately below the penthouse. (4.3)
Niles says he would never presume to fill in for Frasier on his radio show (4.5) but Niles has already filled in for Frasier on his radio show. (1.23)
Maris refuses to go on cruises due to her fear of buffets (4.15) but goes on a cruise when invited. (5.6)
Niles can't leave his apartment at The Montana through the kitchen (4.14) but Marty and Frasier can enter and leave his apartment at The Montana through the kitchen. (10.14)
During a fight about Sherry between Frasier and Marty in the kitchen, the dishes on the kitchen island keep alternating from shot to shot between a black bowl and a stack of white plates. Eventually Marty slams and breaks a white plate but in the very next shot there are no white plates or broken pieces, and the black bowl has returned. (4.19)
Frasier doesn't speak German (2.21) but Frasier speaks German. (8.21)
Niles turns around at the Oregon border check because he's carrying fruit (2.21) but there is no Oregon border check.
Marty says the high temperatures will probably cause brown-outs but Seattle never sees brown-outs since so few homes have air conditioning, including The Montana. (4.21)
Marty "never touches" the answering machine (4.24) but picks up all the messages on the answering machine. (8.15)
Frasier was born in 1952 (7.8) but he was born in 1964 since Queen Elizabeth's only child born in March was Prince Edward, Earl of Wessex. (7.10)
Frasier's birthday is in May (5.23) but he reminds Marty that his birthday is in March (5.8) although his mother records in her journal that she was pregnant with Frasier in April. (4.22)
Despite an electrical problem shutting down the monorail system, another monorail train zooms by in the background. (5.5) The halted train which Frasier and Niles boarded to go to the Space Needle is on the western track which goes only to Westlake Center, away from the Space Needle.
Niles drops his cup of cappuccino in Pike Place Market but nothing spills out of it on the ground - much less onto Frasier's suede shoes, immediately requiring him to buy another pair. (5.5)
Niles' dry cleaner is Mr. Lee (5.9) but his dry cleaner is Mr. Kim. (3.7)
There is no zoo on Mercer Island. (5.12)
Frasier has never had a patient fall in love with him (5.13) but Frasier has had patients fall in love with him, (9.3) thirteen in fact. (11.19)
Niles says tells Caitlin it was nice to meet her but Niles had already met her. (5.19)
Frasier can't have guests because of a small scratch on his hardwood floor (3.5) but he can have guests despite a large, unsightly piece of tape covering a crack on his living room window. (6.8)
Upon meeting Marty, Woody says he recalls hearing Frasier say his dad was a policeman (6.13) but when Sam meets Marty he recalls hearing Frasier say his dad was dead and formerly a scientist. (2.16)
There is no British Consulate in Seattle. (6.17)
Daphne has no other formal dresses but the one the dry cleaners ruined (6.17) but she has several other formal dresses. (3.13 and 2.18)
The Laureate Luncheon bidding sheet at the Kelly Anne Grunther Foundation Annual Auction is in two places at the same time: at the bidding table and at the auctioneer's podium. (6.19)
Roz wants to be Frasier's date for Daphne's wedding (7.21) but Roz doesn't want to be Fasier's date for Daphne's wedding. (7.23)
A rolling head of cabbage appears out of nowhere when Regan drops her bag of groceries in the hallway. (7/20)
Marty is surprised to learn Daphne knew Niles was in love with her (7.24) but he already heard it directly from Daphne. (7.10)
Eddie can't stay at The Montana because dogs aren't allowed (6.3) but Eddie stayed at The Montana while Frasier refinished his floors. (8.7)
Dr. Mary has a call-in radio show on KPXY (7.16) but Dr. Mary's call-in radio show is on KEZW. (8.8)
Frasier and Niles went to John Adams Junior High School (2.11) but Frasier and Niles went to Bryce Academy. (9.5)
Roz didn't know the station had a line 7 (9.8) but Roz knew the station had lines 1 through 8. (1.4)
Frasier says remembering how to break into his old house is as easy as remembering how to ride a bicycle (9.19) but Frasier doesn't know to ride a bicycle. (10.16)
The scariest words of Niles' childhood were "Your father needs your help down in the basement," (9.22) but their house had no basement. (9.19)
Frasier believes that superstitions are unhealthy (10.4) but Frasier believes he's cursed, a strong superstition about his high school reunions. (6.2)
Jason, the kid trick-or-treating at The Montana (10.5) was a trick-or-treater at the Elliott Bay Towers the year before. (9.6)
Freddie turns thirteen in 2002 (10.6) but Freddie was thirteen in 2000 despite being born in November, 1989. (8.10)
Niles flipped a coin 17 times and got a blister (10.7) but Niles doesn't know how to flip a coin. (6.21)
Niles is unable to grow a mustache (6.20) but has no trouble quickly growing a goatee. (9.1)
Daphne's mother immediately believes it when someone says Daphne is pregnant (7.24) but Daphne's mother believes Daphne is a virgin. (9.13)
Frasier has never seen the inside of the Empire Club (10.9) but Frasier has seen the inside of the Empire Club. (2.18)
Niles never had any girlfriends before Maris (3.13) but Niles had a girlfriend in college. (11.8)
Niles knows exactly what Spackle is (10.12) but Niles doesn't know what Spackle is. (11.9)
The mighty pixie radio station is KPX (8.9) but the radio station is KPXY. (10.23)
Eddie's birthday is May 7th (5.8) but Eddie's birthday is May 15th. (11.23)
Martin was shot going through a door from a dark alley (1.11) but Martin was shot in a convenience store. (9.4)
While performing in the radio drama Nightmare Inn, Niles uses the balloon's helium tank for voicing the role of Pépo the Dwarf. But the balloons weren't filled with helium or they'd have floated. (4.18)
While in Canada, Niles spots a sign reading "Have your picture taken with a live bear, 1 mile." but in Canada all roadside distances are shown in kilometers, using the metric system. (1.21)
Niles learned from his school days that nail-polish remover dissolves glue (11.22) but wasn't aware you could use nail-polish remover to dissolve glue. (2.21)
Because she distrusts anything that loves her unconditionally, Maris is unable to have pets (2.12) but Maris keeps two dogs (4.22).
Bebe envisions Roz having a daily segment on Dr. Clint Weber's medical show (5.12) but Dr. Clint Weber's show hasn't started yet (5.17).
Contrary to what Gil says in "Ham Radio" (4.18), there are no fens in Surrey. They are in Cambridgeshire, Lincolnshire and Norfolk, over 100 miles away.
Donny, a Seattle-based lawyer, launches a breach of contract lawsuit against Daphne Moon for backing out of their wedding. It is noted that the suit sought "$100,000 in punitive damages". Washington State does not allow for punitive damages in its courts. Only cases heard in Federal Court are eligible for punitive damages in the State of Washington.
The view of the Seattle skyline from Frasier's high-rise condo is an impossible view. The angle of the view, with the Space Needle in foreground and the skyscrapers in the background, is from north of downtown Seattle looking south. There are no high-rise condos north of the Space Needle, just one very massive hill, Queen Anne Hill. In order to get the view that he has, Frasier would need to have a ground-level house about halfway up the side of Queen Anne Hill.
Frasier watched his babysitter and her boyfriend through his home's staircase banister (11.4), but his home had no upstairs (9.19).
Martin and Daphne go shopping together for underwear (1.20) but Martin has no idea that Daphne buys him underwear (10.7).
Martin first met Hester at a crime scene over the chalk outline of a murder victim (2.8) but Martin was first introduced to Hester by Stan Wojadubakowski (7.17).
The great beauty of Frasier and Niles' high school is named Lorna Ann Gardener, née Lynley (7.14), but her name is Lana (8.21).
Because of his feelings for his ex-wife Lorna (Lana), Bob Gardener wondered whether to "break things off with" Kathy, his 22-year old receptionist (9.1), but he was married to Kathy just a few months earlier in Tahiti (8.21).
After Roz discovers on Halloween that she's pregnant (5.3) she drinks alcohol on her cruise (5.6) but won't drink alcohol because she's pregnant (5.10).