Another kind of superstition is as follows. They believe the dead walk by night and feed upon _guarina_, a fruit resembling the quince, but unknown in Europe. These ghosts love to mix with the living and deceive women. They take on the form of a man, and seem to wish to enjoy a woman's favour, but when about to accomplish their purpose they vanish into thin air. If any one thinks, upon feeling something strange upon his bed, that there is a spectre lying beside him, he only needs to assure himself by touching his belly, for, according to their idea, the dead may borrow every human member except the navel. If therefore the navel is absent, they know that it is a ghost, and it is sufficient to touch it to make it immediately disappear. These ghosts frequently appear by night to the living, and very often on the public highways; but if the traveller is not frightened, the spectre vanishes. If, on the contrary, he allows himself to be frightened, the terror inspired by the apparition is such that many of the islanders completely lose their heads and self-possession. When the Spaniards asked who ever had infected them with this mass of ridiculous beliefs, the natives replied that they received them from their ancestors, and that they have been preserved from time immemorial in poems which only the sons of chiefs are allowed to learn. These poems are learnt by heart, for they have no writing; and on feast days the sons of chiefs sing them to the people, in the form of sacred chants.[24] Their only musical instrument is a concave sonorous piece of wood which is beaten like a drum. [Note 24: Commonly called in the native tongue _arreytos_. Some specimens exist. Brasseur de Bourbourg in his _Grammaire Quiché_ gives the _Rabinal Achi_.] It is the augurs, called bovites, who encourage these superstitions. These men, who are persistent liars, act as doctors for the ignorant people, which gives them a great prestige, for it is believed that the zemes converse with them and reveal the future to them.