This is true art. I don't understand it (well, probably nobody) but i have thousands of feelings and something which there is no equivalent word for in english, but seems to be something like anticipation, premonition or foreboding
Does this have to do with the relativity of being captive? I mean, you can also see it as if the world outside the circle is trapped by the circle. Animals around it wonder what is inside, but ignore the rest of their "extense" world. You can be trapped although you have plenty of space to move.
I know it's really symbolic, but I can't help also ponder this scene literally as a huge entity or artifact out in a field, really containing nothing but raw evil.