Melissa's thumb sucking is actually two independent responses to a traumatic event. It could be both responses present at once, or it could be one or the other, however, this can not be properly analyzed without a psychiatric analysis. The two responses thus far that can be inferred are: a reverting back to an infantile state as a coping or avoidance mechanism, and/or a Post Traumatic Stress Disorder induced reaction that is either a coupling to the infantile state or completely independent of it.