As Esther comes down the stairs to the party in the parlor
(with John Truett as one of the guests), she passes by the grandfather clock on the landing. In the shot just before coming to the landing, the pendulum is swinging. In the next shot, Esther is on the landing, and the pendulum is stopped.
In the supper scene when they are trying to rush the meal so that Rose can take her long distance call in private, Katie the maid serves Mr. Smith his soup. The bowl looks completely empty through the whole scene until Katie comes to pick up the bowl. At that point, it is full of brightly-colored soup.
After Tootie finishes singing "I was drunk last night, dear mother" you can see and hear Esther (Judy Garland) begin saying a line: "Tootie, you're a very bad--". The shot immediately changes to a closeup, and she repeats the line, this time more audibly and in its entirety: "Tootie, you're a very bad girl!"
After Lon's going away party when Esther gave John back his hat, he found raisins in his hat. He then walked outside, but after Esther called him back it appears that John is no longer holding the raisins.
Early in the movie the father mentions the Baltimore Orioles. By mid-1903 (the approximate time at the beginning of this movie) there was no major league team named the Baltimore Orioles. The 1901 American League Baltimore Orioles were the New York Highlanders in 1903 (later the New York Yankees in 1913). Ironically, the Baltimore Orioles of today were the former St Louis Browns in 1902. The team moved to Baltimore before the 1954 season.
It is often incorrectly claimed that an off screen male voice calls out "Hiya, Judy" (referring to actress Judy Garland instead of her character, Esther). The voice actually says "Hiya, Johnny". This refers to Tom Drake' s character, John Truett, who has been trying to catch the trolley and apparently just made it. As soon as the line is delivered Esther looks expectantly screen right but we do not see John until the end of the trolley song sequence.
The goof item below may give away important plot points.
When Esther and John are looking out over the fair at the end, John remarks that he liked it better when it was a swamp and it was just the two of them. They didn't actually meet until the night before the trolley trip to see the fairgrounds, already in progress.