Notwithstanding the fact that we are dealing with a chorea--that is to say, with a disease which is almost as readily recognisable by the public as by any professional--the difficulty of fixing its onset is paralleled by the difficulty of knowing when it has ceased. This uncertainty is explained by the facile and changeable nature of the patient; until the condition is revealed by unmistakable signs it passes for an insignificant muscular caprice of no pathological importance, while its disappearance is not associated with any particular modification of the patient's ways. There is a natural tendency to identify all "nervous movements" with myoclonus, but the conception is a remarkably nebulous one, and means nothing more than "muscular twitch." On the other hand, it is well understood that "nervous movements" are more or less sudden movements of limbs, shoulders, face, always involuntary and generally increasing in force and frequency with the nervous state of the patient. Parents say, for instance, that their child has become more restless and irascible, and at the same time that he has had "more movements of the nerves." The coincidence is unfailing. Is the expression "nervous movement" lacking in precision? Yet it signifies what it is intended to signify. We are concerned neither with tonic convulsions nor with clonic spasms, nor yet with tics of habit; what the term stands for is a complex contraction, brisk but not violent, closely allied to the simplest of automatic acts, such as a step in advance, a shrug of the shoulders, a frown, a sigh, a moan, a crack of the fingers, an exclamation--in any case usually a gesture of impatience. The whole thing, however, is so variable and fugitive, that it cannot be said to constitute a definite convulsive phenomenon. The contractions, further, in spite of their complexity, escape the notice of their originator, who is quite surprised at being asked the meaning of the movement he has just made, as he is almost entirely ignorant of it. Briefly, the "nervous movements" of which we have been speaking do not belong either to myoclonus or to tic, but owe their distinctiveness to their multiplicity and inconstancy. At the same time they are always grafted on a certain neuropathic diathesis akin to that of chorea; in fact, they are nought else than a form of chorea themselves. The psychical peculiarities of the patient with variable chorea may be summed up in instability of thought and action, combined with mental infantilism. Hence the terms "polymorphous chorea" and "chorea of degenerates" are used synonymously for variable chorea.[138] Sometimes the disorders of the mind include hallucinations, and various forms of phobia or mania. One or two examples may be given: