After four hours of torture, the Apache and the other two
cops threw a bucket of water at the prisoner to wake him up
and said: "The Colonel has ordered us to tell you you're to be
given a chance to save your skin. If you guess which of us has
a glass eye, you'll be spared torture." After passing his gaze
over the faces of his executioners, the prisoner pointed to
one of them: "His. His right eye is glass."

And the astonished cops said, "You're saved! But how did
you guess? All your buddies missed because the eye is
American, that is, perfect." "Very simple," said the prisoner,
feeling he was going to faint again, "it was the only eye that
looked at me without hatred."

Of course they continued torturing him.

Roque Dalton

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