Whenever Lam., who exhibits incessant balancing and rotatory movements of the head, is seated in proximity to a wall, he knocks his head sideways against it until a bruise results, and appears to find therein a source of genuine satisfaction.[24] If, then, an obsession provokes a motor reaction at all, it may originate a tic, and, in the case of tonic tics, this is a very common mode of derivation, as one may well understand how an obsession may occasion an attitude. Grasset cites the example of a young girl who would never lean backwards in a railway carriage or on any chair or bench, preferring to sit bolt upright on the edge. In this instance the adoption of a stereotyped attitude was directly attributable to an obsession. Another example of an attitude tic is furnished by the case of young J.: Standing or seated, he always has his half-flexed left arm firmly pressed against the body in the position assumed by hemiplegics. Its pose and inertia and the awkwardness of its movements unite to suggest some real affection, the existence of which the constant use of the right arm and the elaboration by the patient of intricate devices to obviate disturbing the other tend to substantiate. Nevertheless, the impotence is entirely imaginary. To order he can execute any movement of the left arm with energy and accuracy; his left hand will button or unbutton his clothes, lace his boot, handle a knife, and even hold a pen and write. It seems that the position of the arm was chosen deliberately to alleviate a supposed pain in the shoulder, and unceasing resort to this subterfuge of his own inventing, which he considered a sovereign remedy, ended in its voluntary adoption being succeeded by its automatic reproduction.