Follow the Curve

I think a rounded-edge is the hardest part of an origami piece.  By nature, folds are straight and sharp, so to create the effect of a smooth, round curve requires some extra work.  Looking at the origami piece above, you can see how I created the rounded tops of the heart by combining many little folds.  To make the edge look smoother, I would add more folds so that the straight fold-edges become smaller and smaller; as the straight folds become smaller, the illusion of a curve becomes clearer.  This effect is especially useful in animal origami, as very few animals have straight features.