When Danny Kay and the younger sister (of the Hanes sisters) are dancing on the dock when their two groups first meet. Watch closely toward the end of that scene. As Danny Kay is on one knee and he brings her around him in a circle, she trips on his foot, but continues on as if nothing ever happened.
if im not mistaken, in those days if there was a mistake in a movie, to fix it, they would have had to redo the whole movie up to that point. so for her to trip probably wasnt a big enough mistake to redo that much of the film.
thats what i heard, i dont know how true that is though.