Revealing mistake: Rob and Laura are both freaking out and panicking in their bedroom when all of a sudden Jerry shows up outside their closed window. Yet Jerry puts his arms in their room, showing it's not an actual window.
Deliberate mistake: Rob is about to leave his room, and he opens the bedroom door to the noise of a loud music box that was originally being made by Laura's music box that holds jewellery in it.
Factual error: While Rob is roaming the house with a gun in his hand he chops the metal tube that the wood burning stove in the living-room is connected to. However since in real life the metal tube would be thick and insulated the tube he dented with his hand at that speed wouldn't have been damaged at all. Also, it could have broken his hand or at least sprained his hand where he wouldn't be able to use it or feel like using it.
Will You Two Be My Wife? - S2-E17
Revealing mistake: While Rob is asking for 2 passes for 3 days in the Captain's office the plant that is outside the "closed window" behind the open blinds has leaves can be seen in between each of the blinds. Which means that the tree isn't actually outside and there is no window, just a window frame. (00:04:40)
Continuity mistake: When Laura tries to read the phone number that Rob scratched out, Rob gives her the number as "New Rochelle 69970," which happens to be the Petrie's own phone number, as noted in other episodes.
It May Look Like a Walnut! - S2-E20
Character mistake: Rob is having a nightmare, part of which involves the disappearance of his thumbs. When he finds Laura at home, the script calls for him to say, "I want you to help me get my thumbs back," but he actually says, "I want you to help me get my thumb backs." His thumbs are also still there but hidden (you can see a portion of them in one frame of the episode).
It May Look Like a Walnut! - S2-E20
Continuity mistake: The episode opens with Rob watching a horror movie on television. The bedside clock shows the time as 9:05. At the end of the episode 23 minutes later, the clock shows 9:10.
Don't Trip Over That Mountain - S2-E22
Character mistake: Laura tells Millie that the phone rang 6 times. The phone actually rang 7 times.
Continuity mistake: When Rob is trying to draw the horse and accidentally draws on the wall, the drawing changes depending on the shot.
A Surprise Surprise Is a Surprise - S2-E30
Factual error: Buddy asked Sally "why haven't you had a birthday...?" Yet a few episodes ago (Season 1 Episode "Where you been, Fassbinder?") Sally had a birthday she cried and cried. Buddy and Pickles, Rob and Laura were all there.
When a Bowling Pin Talks, Listen - S2-E32
Continuity mistake: Buddy poked the punching bag with Mel's face on it. Then later Mel comes in when the delivery service guy comes. Mel's face is aiming towards the wall. His face on the punching bag keeps appearing and disappearing every time we jump cut from the writers and the delivery guy.
The Ballad of the Betty Lou - S3-E9
Other mistake: While Jerry and Rob are furious, Jerry asks the sailor "What's the matter with the lights?" and the sailor says "power failure on the line, they can't locate it." If there's a power failure then the room would be completely dark just like it is outside. Yet Rob and Jerry have shadows on their hats, jacket, shirts etc. as well as a shadow from the bunk bed. These shadows are caused by the non-working lights or the lights behind the camera.
The Sound of Trumpets of Conscience Falls Deafly on a Brain That Holds Its Ears - S3-E11
Other mistake: Rob is complaining to Sally and Buddy about this couple running through a parking lot not looking where they are going, and they knocked him down on his rear end as well as hands. He fell into some grease yet there weren't any grease stains on his jacket which would have actually been on his butt and hands.
My Husband is the Best One - S3-E14
Continuity mistake: In a different episode the Alan Brady show writers were on a different floor than Alan Brady and Mel Cooley. Yet in this episode they're on the same floor because we can hear Alan yelling at Mell while Rob is in the writers room where Sally and Buddy, currently furious reading the magazine article. (00:14:37)
Happy Birthday and Too Many More - S3-E15
Other mistake: Laura is doing some work on when to have Richie's birthday, and Rob tells Laura "I thought we decided that about 8 years ago." Yet Mrs Billings has asked Rob to do 2 plays (1 each year for the PTA meetings) In the Happy Birthday... (Feb 1964) episode that would have made Richie about 10 due to the fact that Richie was 8 when "What's in a middle name" (Nov 1962) aired. (00:01:00)
The Lady and the Tiger and the Lawyer - S3-E16
Continuity mistake: Donna goes back to the den to get her coat to show Arthur. Laura yells at Rob in the kitchen "Rob! Did you lock her in the Bathroom!?" It's a den in most of the episodes... Turns out in this episode it turns into a bathroom with carpet on the floor. (Supposedly when Laura is yelling at Rob in the kitchen).
The Life and Love of Joe Coogan - S3-E17
Other mistake: When Rob, Buddy, Sally, Joe and Mel are all showing up after they played golf at the beginning of the episode if you look at the window all the background there is flat as heck. But trees do not increase in elevation that quickly in flat ground. Unless you're in the mountains.
The Life and Love of Joe Coogan - S3-E17
Other mistake: Rob is discussing the box of love letters with Laura she tells him "they're by the furnace!" Rob tells her "there's no shoe box by that furnace." Laura tells him "they're right behind some loose bricks" well when we see the basement... There's no furnace or bricks anywhere to be seen.
A Nice, Friendly Game of Cards - S3-E18
Character mistake: While Rob, Laura, Buddy, Jerry and Millie are telling Sally what happened before and during the poker game Laura says "We should have played charades!" Yet she didn't actually say that... Rob said it. Jerry insisted they play poker anyways.
A Nice, Friendly Game of Cards - S3-E18
Other mistake: With the way everyone was holding their cards, there is no way Rob could have been reading the back of everyone's cards.
