The trial started the moment Eshe crossed an infrared light beam in front of an aperture positioned directly in her running path. The opening, flanked by the small arms of two T-shaped metal bars protruding from each side of the chamber, defined a slot through which Eshe had to pass to reach the opposite wall. Her job was far from trivial: in total darkness she had to estimate, in a single attempt, the aperture's diameter as quickly as possible. To make things more complicated and interesting, the opening's size varied randomly from trial to trial. Without being able to see the bars, Eshe had only one way to achieve her goal--she had to rely entirely on her exquisite sense of touch.