 David Knipe theorizes Iðunn 's abduction by <unk> in eagle form as an example of the Indo @-@ European motif " of an eagle who steals the celestial means of immortality . " In addition , Knipe says that " a parallel to the theft of Iðunn 's apples ( symbols of fertility ) has been noted in the Celtic myth where Brian , <unk> , and <unk> , the sons of <unk> , assume the guise of hawks in order to steal sacred apples from the garden of <unk> . Here , too , there is pursuit , the guardians being female griffins . " 
