Is to discover a deception at the moment, for some is to anticipate the danger. The origin of the phrase is not clear. Borges supposed that the Knave was a letter of ill omen and that it was brujuleaba from below; Other linguists believed to see a misinterpretation of "see the pints to the Jack" to know the stick, without explaining why to the jack, or for what; They also came to play Sota by his sense of Casquivana woman, since in the past the respectable ladies did not raise their skirts to show the legs. Maybe it is related to the card games, where you had to show the winning hand and some cunning tried to pass a jack by horse overlapping the cards. And is that from above (if we can disguise the detail of the number) both figures are alike, but from below the legs of the Jack have shims, and those of the horse, helmets.