Delouvrier closed his eyes. "There was a man, a blind man, who mastered echo-location. Clicks with the tongue, you understand?" Eyes closed, he demonstrated. "Like a bat. Fantastic." He opened his eyes. "He could perceive his immediate environment in great detail. Ride a bicycle in traffic. Always making the tik, tik . The ability was his, was absolutely real. And he could never explain it, never teach it to another..." He wove his long fingers together and cracked his knuckles. "We must hope that this is not the case with you."