cockatrice, in the legends of Hellenistic and Roman times, a small serpent, possibly the Egyptian cobra, known as a basilikos (“kinglet”) and credited with powers of destroying all animal and vegetable life by its mere look or breath. Only the weasel, which secreted a venom deadly to the cockatrice, was safe from its powers.
By the beginning of the 17th century more marvels had been added to the legend. The snake was said to be generated from an egg laid by a cock and hatched by a serpent. In addition to the weasel, another enemy was the cock; if the basilisk heard a cock crow, it would shortly die. Thus travelers in regions allegedly infested by the basilisk took cocks with them.