Hmm. Well, first, I'm glad you guys liked the story and the writing so much! A bit surprising, too, since that wasn't really my focus. I may try a dialogue-driven game next LD.
Looking back on it now, giving the player a button and saying "figure it out" probably wasn't the best way to introduce them to this mechanic. In a nutshell, everything that's not visible from the focus point is nonsolid in the grass world. So, normally, everything in the grass world seems to be solid, since, if you can collide with it, you can probably see it. When you put down the focus point, everything that you can't see in the grass world is no longer solid, so you can pass through it.