Continue to the right, ignoring the hanging boxes for a moment and continue into the cave. Climb the ladder here and jump to the box with the bird sitting on it, jump up and down on the box until the rope snaps.

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Jump onto the crate with the bird on it (left) and then push it up to the wall on the right (right) to access the platform above.

Now that the crate is at ground level, push it as far to the right as you can. Now use it to jump up to the ledge above.