I noticed last week that Taken Thralls can't see you if you don't move. Sort of like a T-Rex. It was at the Oryx checkpoint in the raid. Just stood still, and the thralls walked right passed me. Didn't even look at me. Tried it again, and they didn't look at me for a little while. Eventually, though, they started beating the living crap outta me. So I'm guessing it only works about 90% of the time. But still, I just thought I'd put this out there.