Rails (6)
I believe the answer is:
tracks
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rails</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know this)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tracks that I've seen before include "Rough paths; traces" , "Spoo" , "Follows the marks of an animal" , "Parallel rails" , "Marks left in ground by animals" .)