In conjunction with our earlier work (Schachter, 1971a), the various studies presented in this monograph have consistently demonstrated an association between obesity and external sensitivity. Though there is the implication in our speculations that externality leads to obesity, we have meticulously avoided consideration of causality, for from the experiments proper there is no more reason to assume that externality causes obesity than that the reverse is true. Indeed, on a common-sense level, one can make a very good case for the proposition that these experiments tell us very little new or interesting but simply spell out the consequences of being fat. After all, the obese animal, human or rat, has an immense reserve of food energy. He may be more finicky and less responsive to internal cues because he can physiologically afford to be so. Similarly, when unstimulated he may move less simply because it's harder to do so. Though such an explanation can by no means account for all of the facts (e.g., emotionality, active avoidance learning, etc.), it does seem such simple good sense that despite its irritating banality, it cannot be dismissed out of hand. Because the matter is, in a sense, crucial to the interpretation ofthis entire body of data, we will in this chapter digress from the general theme of the monograph in order to consider the implications of our analyses and experiments for the causal question.