As Uncle Sid prepares to go onto the "field of honor" in the beer drinking contest, he has a mug full of dark beer. It changes to a lighter-colored amber beer in the next shot.
(around 78 minutes) When Muriel sneaks out of the house to meet Richard, she is wearing a blue scarf. But when it cuts to a shot outside the house the blue scarf has changed to a shorter length. When she arrives at the brook to meet Richard, the blue scarf has changed back to the original length.
At the beginning of the "Stanley Steamer" segment Richard Miller (Mickey Rooney) lights the burner in the steamer then gets in and drives away accompanied by several explosions from under the hood. A Stanley Steamer took several minutes to develop steam and could not be driven immediately, also there was nothing under the hood but a burner and a boiler neither of which would cause explosions of the type shown.
Both the man and the woman portraying the "American Gothic" couple cast shadows on the background as they step into frame, revealing the house behind them is a painted flat.
All of the flags shown celebrating the 4th of July 1899 are 48-star flags, not introduced until 1912. In 1899 there were 45 stars in the flag.