The fact that the basis of a smile is a movement of the mouth at once suggests a connection with the primal source of human as of animal enjoyment; and there seems, moreover, to be some evidence of the existence of such a connection. A baby after a good meal will, I believe, go on performing something resembling sucking movements. The first smiles may have arisen as a special modification of these movements when there was a particularly lively feeling of organic contentment or well-being. I believe, further, {172} that an infant is apt to carry out movements of the mouth when food is shown to it. A similar tendency seems to be illustrated by the behaviour of a monkey which, when a choice delicacy was given it at meal-time, slightly raised the corners of the mouth, the movement partaking of the nature of “an incipient smile”.[108] Again, our hypothesis finds some support in the fact that, according to Preyer and others, the first smiles of infants were noticed during a happy condition of repletion after a good meal.[109] Supposing the smile in its origin to have thus been organically connected with the pleasurable experience of sated appetite, we can easily see how it might get generalised into a common sign of pleasure. Darwin and Wundt have made us familiar with the principle that expressive movements may be transferred to states of feeling resembling those of which they were primarily the manifestations. The scratching of the head during a state of mental irritation is a well-known instance of the transference. There are, I believe, facts which go some way towards verifying the supposition of a transference of eating-signs to states of lively satisfaction and pleasure generally. Savages are wont to express keen pleasure by gestures, _e.g._, rubbing the belly, which seem to point to the voluminous satisfactions of the primal appetite. The clearest evidence, however, seems to be furnished by the account of a baboon given us by Darwin. This creature, after having been made furiously angry by his keeper, on making friends again, “rapidly moved up and down his jaws and lips and looked pleased”. {173} Darwin adds that a similar movement or quiver of the jaws may be observed in a man when he laughs heartily, though with us the muscles of the chest rather than those of the lips and jaws are “spasmodically affected”.[110]