" this deer hunt was then only a cunning trick of the enemy ! " said the prince , looking round on the flames and the smoke that crackled and rolled in towards him on every side . " what a fool i was to be lured into this trap like a wild beast ! " and he ground his teeth with rage as he thought of the governor 's smiling treachery . dangerous as was his situation now , the prince was not in the least confounded . in his dire extremity he remembered the gifts his aunt had given him when they parted , and it seemed to him as if she must , with prophetic foresight , have divined this hour of need . he coolly opened the flint - bag that his aunt had given him and set fire to the grass near him . then drawing the sword of murakumo from its sheath he set to work to cut down the grass on either side of him with all speed . he determined to die , if that were necessary , fighting for his life and not standing still waiting for death to come to him . now the prince ascribed his escape entirely to the virtue of the sword of murakumo , and to the protection of amaterasu , the sun goddess of ise , who controls the wind and all the elements and insures the safety of all who pray to her in the hour of danger . lifting the precious sword he raised it above his head many times in token of his great respect , and as he did this he re - named it kusanagi - no - tsurugi or the grass - cleaving sword , and the place where he set fire to the grass round him and escaped from death in the burning prairie , he called yaidzu . to this day there is a spot along the great tokaido railway named yaidzu , which is said to be the very place where this thrilling event took place . 
he used the sword to cut the grass .
why did yamato rename the sword to the grass-cleaving sword ?
why did yamato rename the sword to the grass-cleaving sword ?