and , to the young man 's horror , as soon as their lips had met , an awful change came over her . for her beautiful mantle and riding - skirt of silk seemed to fade away , leaving her clad in a long grey garment , which was just the colour of ashes . her beauty seemed to fade away also , and she grew old and wan ; and , worst of all , half of her abundant yellow hair went grey before his very eyes . she saw the poor man 's astonishment and terror , and she burst into a mocking laugh . " i am not so fair to look on now as i was at first , " she said , " but that matters little , for thou hast sold thyself , thomas , to be my servant for seven long years . for whoso kisseth the fairy queen must e'en go with her to fairy - land , and serve her there till that time is past . " when he heard these words poor thomas fell on his knees and begged for mercy . but mercy he could not obtain . the elfin queen only laughed in his face , and brought her dapple - grey palfrey close up to where he was standing . " no , no , " she said , in answer to his entreaties . " thou didst ask the kiss , and now thou must pay the price . so dally no longer , but mount behind me , for it is full time that i was gone . " so thomas , with many a sigh and groan of terror , mounted behind her ; and as soon as he had done so , she shook her bridle rein , and the grey steed galloped off . on and on they went , going swifter than the wind ; till they left the land of the living behind , and came to the edge of a great desert , which stretched before them , dry , and bare , and desolate , to the edge of the far horizon . at least , so it seemed to the weary eyes of thomas of ercildoune , and he wondered if he and his strange companion had to cross this desert ; and , if so , if there were any chance of reaching the other side of it alive . 
he needed to pay for the price of kissing her .
why did thomas listen to the queen of fairies and mounted behind her ?
why did thomas listen to the queen of fairies and mounted behind her ?