Deliberate mistake: Throughout the movie we hear every animal (and insects/arachnids as is the case with Charlotte and her offspring) with one exception. Every time Charlotte catches her meals in her web we never hear the fly or other insect she is descending upon cry for help, or plead with her to be spared. This is deliberate due to this being a kid's film but still bears noticing as a mistake due to the fact that they are the only ones rendered mute for plot convenience.
Charlotte's Web (1973)
1 deliberate mistake - chronological order
Directed by: Charles A. Nichols, Iwao Takamoto
Starring: Debbie Reynolds, Paul Lynde, Henry Gibson, Rex Allen
Continuity mistake: When Fern is celebrating Wilbur's two-week birthday, he is much smaller in size than in the song scene that played prior to the birthday.
Charlotte: Trust me, Wilbur. People are very gullible. They'll believe anything they see in print.