but when , drawn by the amiable look of their reflections , they had crossed the shimmering sheet and found themselves in total darkness ( for somehow gallan had lost the glowstone he was holding ) , whose cold , thick air was fraught with odors they had never smelled before when , in short , they realized that , just as their makers had warned them years ago , by entering the mirror mountain theyd been expelled from lurien forever , they instantly became as beasts , howling and beating their fists against the unseen wall of rock into which the shining threshold had disappeared .