Personally, I don't think that it's so much a combination of vines needed, as a certain amount of strength. It seems to me that when you are holding ALL the vines (more than you need), Gilly starts first with the weakest ones and uses only as many as she actually needs, eliminating/not using the stronger ones.
It's as if you are holding 10 1-foot pieces each of thread, string, yarn, cord, and rope. You only need to go 30 feet, so you'll use 30 pieces.... if you start with the thread and the string and yarn, you'll have 30 weak pieces and discard the ones you don't didn't use-- the strong ones.
If you drop the thread and string and yarn, and only hold the cord and the rope, then she'll start with cord, then go to rope and, you'll have the strongest rope available. Well kind of, I mean it's a strange analogy that wouldn't work in real life, but it's the best way to explain the way I understand it.
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With that perspective/opinion stated, I'll add that the "helpful vines hint" posted in the official first post seems overly complicated to me with the counting, going back, dropping one kind, trying the next kind.
I collected ALL of the vines. Dropped them in neat piles all in one "room." Then I followed this plan:
Pick up one complete pile to see the message (strong, weak, almost strong enough, etc). Make a note of whether that pile was strong, weak or medium. Drop that pile.
Pick up the next complete pile, repeat until you know strength of all piles. The nice thing here is that you only have to pickup-putdown 6 times, instead of trying piece after piece after piece.
Now, pick up the two strongest complete piles.
When you see the cliff, you can get an idea how many more pieces you need by looking at how big they are and how far the rope is from the bottom -- but don't pick up too many or you'll have to start over! For instance, if you think you need three, pick up only one. If you see you need probably 6 more, pick up only 3.
also, here again is my map of the middle (vines) woods, for people to check with theirs and see if it's compatible.
http://www.thedrehers.net/high-woods.gif