They did what to us?

Zinjanthropus over at A Primate of Modern Aspect mentioned Robert Sapolsky's book A Primate's Memoir in a post last month. It sounded great ("one of the most beautiful books I have ever read, and I really don’t think it’s because I am a primate geek. I think it’s one of the rare science books that would be enjoyable for anyone, or maybe everyone, to read.") so I picked it up (on the Kindle, yay!) and have been reading it this week. It is great - it's exciting and funny and, yes, beautiful.

But here's a usage that throws me. He's talking about how the baboons he's studying occasionally head off into "the Great Impenetrable Thicket", where they can't be followed. The grad students he took over from said that "inventing the wheel" must be

what the baboons must be up to when they thicketed us.

That's impenetrable on its own. Without the explicit context of the paragraph, I'd take "to thicket us" as meaning "to put us in a thicket", not "to hide from us by going into a thicket". I'd have had to use the adjunct of disadvantage structure here, and said "when they thicketed on us".