Continuity mistake: When the men put Curley and Laurie on the haystack after their wedding, the cowboy with the green shirt and cream waistcoat (who gives Laurie the 'girl baby') is wearing a hat, then he isn't, then he is. Also, when the men are told to get water, in the close shot he runs off, then in the zoomed out, he goes again.
Continuity mistake: Just before "Many a New Day", when Laurie enters the house, there are two women discussing the fact that Curley has "taken up with that Cummings gal", the girl with the long, black hair gasps and looks at Laurie. Notice how straight her hair is: it is completely straight except for a few curls at the very bottom. Later on during the same song, when Laurie sings "many a light lad may kiss and fly", the same girl walks into the shot, and her hair is now very wavy. The amount of waves in her hair changes repeatedly until the end of the song.