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.
The Dick Van Dyke Show (1961)
1 revealing mistake in A Bird in the Head Hurts - chronological order
Starring: Dick Van Dyke, Mary Tyler Moore, Morey Amsterdam, Larry Mathews, Rose Marie
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).
Laura Petrie: You wanna end up another Dwight Heatherton, go ahead.
Rob Petrie: Who's that?
Laura Petrie: Dwight Heatheron happens to be an excellent writer who is unknown because he gets no publicity.
Rob Petrie: Then how do you know him?
Laura Petrie: Oh Rob, he's famous.
Harrison B. Harding of Camp Crowder, Mo. - S1-E6
Trivia: Rob tells the police over the phone "Get a prowl car to 148 Bonny Medow Road." 148 was also Dick Van Dyke's weight during the TV series.