There are a few places it could fit in the background:
(1) when R2 is looking into Yoda's hut while it's raining
(2) when Luke is moving about on the vines (or more specifically after he comes back down to the ground)
(3) when Luke approaches and enters the tree
The main thing is giving the impression that even the trees can get up and uproot themselves, ie EVERYthing on Dagobah is alive, squirming and moving.