Quest for Colours - need help!

[aprildaisy]

I'm far from finishing it...but I have the following:

Spoiler

sock full of water, leaf, paper, parchment, stethoscope,smouldering stick and hay

[close]

and I've not a clue as to where to go next. Anyone know what to do in the room with the shocking force field? The tip was "attend to where to step" but I can't get any of my inventory items to interact with the tree-half. What am I missing?