<p><i>Left</i>: Prehistoric illustration of an elephant from the Libian Tadrart Acacus (<a href="http://www.galuzzi.it" target="_blank">http://www.galuzzi.it</a>, the permission from the photographer, Luca Galuzzi is found in the Supporting Online Material). <i>Right</i>: Contour of the elephant. Here there are three possibilities (A, B, C) for the alignment of the assumed ground line: In cases (A), (B) and (C) the walking depiction falls in cells <i>Be</i>, <i>Cf</i> and <i>Bf</i> of the walking matrix, respectively, all being incorrect.</p
