Apparently, there was a big gum-chewing problem back then. Enough so that a major part of the moral lesson from a major motion picture had to be devoted to discouraging children from doing it.
GUM CHEWING'S FINE WHEN IT'S ONCE IN A WHILE
IT STOPS YOU FROM SMOKING AND BRIGHTENS YOUR SMILE
BUT IT'S REPULSIVE, REVOLTING, AND WRONG
CHEWING AND CHEWING ALL DAY LONG
THE WAY THAT A COW DOES