A Man's Teeth Are Not His Own - S2-E13
Revealing mistake: When Rob is "playing" the piano none of the keys on the piano look to actually be pushed down. Also when he's scratching his back with each of his hands the notes on that same side of the piano are still played. He's not actually playing the piano. (Except for the last 2 notes or chords). (00:02:46 - 00:03:27)
Revealing mistake: When Rob is talking on the radio, and says something along the lines of WOFF the station with (then a long pause while he plays a car sound) drive. The On the Air sign goes off before he says drive. He was still on the air.
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.
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)
Revealing mistake: When the female witness is called to the stand, VERY obvious shadowing of the boom mic when she stands up - you can see it on the wall.
A Bird in the Head Hurts - S2-E11
Revealing mistake: The problem with Rob's story is that he said he shot the bird with the rifle, but the rifle there that Rob is swinging around doesn't have a hole for bullets to come out of. It's a fake.
Revealing mistake: Millie (in Rob's dream) tells Jerry (Doc) that "Big Bad Brady is already dead" yet we see that Brady is up there trying to not move, laugh or breathe. He's still alive if his stomach is still going and moving the whole time. Also when he aims his pistol at Rob, he's aiming it at Rob's hat. Not at Rob's arm. Which is where Rob said he got "shot".
Revealing mistake: If Rob and Laura actually did dye their hands not only would their hands be black but so would their wedding rings. Also, while Laura is "using water" on her hands you can tell she wasn't using water or soap because her hands aren't wet and there isn't any soap to be seen at all... You only see the dish rag. (Same for when Rob does the same thing later on). (00:06:07)
A Farewell to Writing - S4-E33
Revealing mistake: Laura and Millie are inside the "house" and Rob is outside the "house" the door and windows are all closed... Yet we can still hear Rob just as if he was in the house rather than outside.
Revealing mistake: While Rob is having a boxing match and Laura is really mad at Rob. I noticed that some of the punches are actually to the hand region when Rob is in the corner and supposedly gets a boxing glove to the face. They aren't hitting each other that hard either.
The Great Petrie Fortune - S5-E6
Revealing mistake: The great-grandfather Petrie was just Rob Petrie dressed as a really old man. The lamp in the movie is also one that has been in Robs house and Sally's house in a few of the episodes.