Now comes a further development of the concept of relativity. A playful element has been introduced, glide reflexion. Roughly the whole of the top half of the print is the mirror image of the bottom half. The topmost flight of steps, down which a curl-up is crawling from left to right, is reflected twice over, once in the middle and then again in the lower part. On the stairs in the top right hand corner, the distinction between ascending and descending has been eliminated, for two rows of animals are moving side by side, yet one row is going up and the other down.

An exquisitely complex print, the mathematical print grid of which can be found in the book

For fun we are including an English translation of the text which Escher wrote to accompany the original print:

The Pedalternorotandomovens Centroculatus Articulosus was created (generatiospontanea!) out of dissatisfaction with the fact that in nature there are no wheel-shaped creatures which are able to move by rolling. The creature shown here, popularly known as a 'curl-up' is an attempt to fulfill this deeply felt need. Its biological characteristics are still uncertain: is it a mammal, a reptile or an insect? It has an elongated body consisting of horny articulated plates and three pairs of legs, which end in feet similar to the human foot. In the middle of the fat, round head, which has a sharply curved parrot beak, there are two protruding eyes, set on stalks and sticking out from either side of the head. When it is stretched out, the creature is able to move over any substratum slowly and thoughtfully, using its six legs (if need be, it can climb up or go down steep stairs, penetrate thick undergrowth or clamber over rocks). However, as soon as it has to travel any distance along a relatively clear path, it pushes down its head, curls up as fast as lightning, pushing off with its feet, if these are still touching the ground. When it is rolled up it has the appearance of a discus, of which the central pivot is formed by eyes on stalks. By pushing successively with each of its three pairs of legs, it can attain a high speed. As it rolls along, it can pull in its feet at will (for instance when going down a slope or when coasting) and thus freewheel. When necessary, it is able to change back to the walking position in two ways: either, abruptly, by suddenly stretching its body, but then it ends up on its back with its feet in the air, or by gradually reducing speed (using its legs as a brake) and slowly unrolling backwards as it comes to a standstill.