What does the narrator says between 7.17, 7.24? ...are short-footed...their ____ is essential to their survival...<br/><br/><div class='ytl __responsive' style='visibility: inherit; '><iframe class='youtube-player' type='text/html' width='640' height='393' src='https://www.youtube.com/embed/TbG1hrZuwEA?autoplay=0&amp;wmode=opaque allowfullscreen' frameborder = '0'></iframe></div>