Some of us can smile when we work. But I think if these Congolese young women could whistle, they would whistle while work. They would probably be better than Snow White and the Seven Dwarfs, too.
Why would they whistle while they walked home from a hard day in the fields? Their basket of full of produce and food to feed their families. In Congo, food comes from the field and goes directly to the pot for cooking.
In a poor country like, refrigerators or ice boxes are rare except in some commercial establishments. Corn is only saved until it is dried to make flour or meal for cooking.
So these young women are happy. They are smiling and proud of the food they are carrying from their distance farm fields.