ASYMMETRY IN THE LARGEST CONSTRUCTED FORMS
These characters have good construction, BUT notice that the forms that make them up are not perfect ovals or circles. They are ORGANIC shapes, asymmetrical.
Not mirror images left and right, or top and bottom.
This is a hard technique do right. First you have to understand basic construction. Then you have to be free enough that you can draw shapes that are not mathematical, but still look convincingly solid.
The asymmetry has to be subtle, not wild and wonky, without any form at all.
Real things in nature have form, yet hey are not perfectly symmetrical, and a god cartoonist applies this concept to his drawings to make them feel natural. Warm and not clinical.