His vision, from the constantly passing bars,
has grown so weary that it cannot hold
anything else. It seems to him there are
a thousand bars; and behind the bars, no world.

As he paces in cramped circles, over and over,
the movement of his powerful soft strides
is like a ritual dance around a center
in which a mighty will stands paralyzed.

Only at times, the curtain of the pupils
lifts, quietly--. An image enters in,
rushes down through the tensed, arrested muscles,
plunges into the heart and is gone.

Rainer Maria Rilke

http://www.poemhunter.com/poem/the-panther/