And to a plant, human shit is fertiliser. If they don't mind they're dumbasses, seeing as most yukkuris got the point excrement is not a very nice thing to be around (even if it's only bean paste- they still recognise it as being shit most of the time).
And to a plant, what passes for their own excrement also tends to be its fertilizer as well. Yukkuri and plants have something in common: if it is organic, it can be used to nourish them. It's just that yukkuri tend to be much more obnoxious.
Incidentally, plants piss me off. Smug little green fuckers, just sitting there, photosynthesizing... mark my words, they're up to something.
Well they've been at it the last ~4 billion years. I don't mind if they are planning something; it will be beyond the evolutionary capacity of the Human species before they do anything.