The same tendency is revealed in an inane search after precision in the most petty details, the natural result in the case of conversation, for instance, being that its thread is quickly lost in endless digressions and parentheses within parentheses. A score of other mental peculiarities, commonly described as "manias" by the lay mind, are nothing else than fixed or obsessional ideas in miniature, as Grasset says, and he narrates how for a time he himself used to be irresistibly forced, on entering a railway carriage, to divide the figure representing the number of the carriage by the number of the compartment. He further cites the case of an otherwise normal individual, who whenever one foot strikes on a stone raised a little above the level of the ground, is obliged to seek an analogous sensation for the other, and who cannot let one hand touch anything cold without giving its fellow the opportunity of receiving an identical impression. A common impulse is to count the windows in the house one is passing, or the bars of the railings. Sometimes it is a "mania" for setting things straight, or for rubbing out marks in a book; but while these and similar psychical accidents are singularly prone to develop in the subjects of tic, they are not to be considered in any way special to them. Hallucinations, too, and sometimes actual delusions, may form a basis from which springs a motor reaction that passes into a tic. If even the most sane among us (says Letulle) are conscious of a wellnigh invincible propensity to repeat a particular movement or expression or sequence of thought, we can understand how the temptation falls with overwhelming force on such as suffer from persistent hallucinations or fixed ideas. Take, for instance, this woman who utters a shrill cry and waves her hand before her face; the regularity of her action is a sequel to the delusion that possesses her, for in her imagination she is chasing away the birds that would pluck out her eyes. And when at a later stage these visual hallucinations are lost in a progressive dementia, the gesture becomes an incurable tic. Here is another patient: his habits of continually washing his hands, of expectorating as he passes any one, have their explanation in his dread of being poisoned by imaginary foes, and, though subsequent mental disintegration precludes the possibility of the delusion continuing, the trick remains to the end of life.