A man may be absorbed in the deepest thought, and his brow will remain smooth until he encounters some obstacle in his train of reasoning, or is interrupted by some disturbance, and then a frown passes like a shadow over his brow. A half-starved man may think intently how to obtain food, but he probably will not frown unless he encounters either in thought or action some difficulty, or finds the food when obtained nauseous. I have noticed that almost everyone instantly frowns if he perceives a strange or bad taste in what he is eating. I asked several persons, without explaining my object, to listen intently to a very gentle tapping sound, the nature and source of which they all perfectly knew, and not one frowned; but a man who joined us, and who could not conceive what we were all doing in profound silence, when asked to listen, frowned much, though not in an ill-temper, and said he could not in the least understand what we all wanted. Dr. Piderit[903] who has published remarks to the same effect, adds that stammerers generally frown in speaking, and that a man in doing even so trifling a thing as pulling on a boot, frowns if he finds it too tight. Some persons are such habitual frowners, that the mere effort of speaking almost always causes their brows to contract. Men of all races frown when they are in any way perplexed in thought, as I infer from the answers which I have received to my queries; but I framed them badly, confounding absorbed meditation with perplexed reflection. Nevertheless, it is clear that the Australians, Malays, Hindoos, and Kafirs of South Africa frown, when they are puzzled. Dobritzhoffer remarks that the Guaranies of South America on like occasions knit their brows.[904] From these considerations, we may conclude that frowning is not the expression of simple reflection, however profound, or of attention, however close, but of something difficult or displeasing encountered in a train of thought or in action. Deep reflection can, however, seldom be long carried on without some difficulty, so that it will generally be accompanied by a frown. Hence it is that frowning commonly gives to the countenance, as Sir C. Bell remarks, an aspect of intellectual energy. But in order that this effect may be produced, the eyes must be clear and steady, or they may be cast downwards, as often occurs in deep thought. The countenance must not be otherwise disturbed, as in the case of an ill-tempered or peevish man, or of one who shows the effects of prolonged suffering, with dulled eyes and drooping jaw, or who perceives a bad taste in his food, or who finds it difficult to perform some trifling act, such as threading a needle. In these cases a frown may often be seen, but it will be accompanied by some other expression, which will entirely prevent the countenance having an appearance of intellectual energy or of profound thought.