Comment by spc476

I can see it as a bootstrap method. You attach a string to the inside end of the vine that moves forward, and it spools out as the vine "grows":

    ____________________
                        \
    O=string============+   movement of growth ->
    ____________________/

        O = spool of thread

When you see the vine on the other end, you can open the end to get the string, attach the cable to the former spool end, and start pulling the string to pull the cable. You want a light enough string for the vine to pull through, while being strong enough to pull a cable through.