The siren and the centaur are two of the mythological beasts that populate the medieval bestiary. Preserved from ancient mythology in texts such as this, their significance changed in the Middle Ages as they became vehicles for Christian teaching. The siren was still represented as half woman, half bird, with an extraordinary power to lure sailors with their charm. In this text, however, the siren has become a moralizing symbol of vanity. Just as sailors are enticed by sirens, so ignorant and incautious human beings are seduced by pretty voices, when they are charmed by vain desires and pleasures. The centaur also appears frequently in medieval art. A fantastic hybrid from ancient mythology, half horse, half man, whose human appearance from the front conceals a beastly nature behind, the centaur represented the sin of hypocrisy in the Christian tradition.