Ah, yes. It's the trees, actually.

[Angela smiles sympathetically. She was confused, too, until the others explained things to her. She's still confused, to be honest, but at least she has a vague idea of what's happening. She suspects that once she reaches the station, she'll understand a whole lot more.]

I am not sure why they follow us, but they only move when not being observed. [She places a hand on the silvery bark of one of the trees.] If you keep an eye on them they should stay put.