of great interest is the passage in which the nature of the dragons of melko is defined : their evil wisdom , their love of lies and gold ( which 'they may not use or enjoy ' ) , and the knowledge of tongues that men say would come from eating a dragon 's heart ( with evident reference to the legend in the norse edda of sigurd fafnisbane , who was enabled to understand , to his own great profit , the speech of birds when he ate the heart of the dragon fafnir , roasting it on a spit ) .