4.a Together, sonnets 50 and 51 address animality from another perspective than breeding. We find the poet traveling away from the young man, evidently on some mission, and blaming his slow progress on "the beast that bears me" (50. 5). The animal (named indirectly as a horse only in sonnet 51 and finally called a "jade"; 51. 9, 12) is a beast of burden, a working animal. Animal motion, not animal reproduction, is at stake. Animals, of course, are animated, and motility has played an important role in philosophical discourse about them. There are two treatises on the topic in the Aristotelian corpus: one on animal movement in general, including growth, decay, and involuntary motion, and one on animal progression through space. We are told in The Movement of Animals that they exercise their power through the expansion and contraction of spirit, which is conserved by the soul in the center of their bodies (703a, 11–24). The motion of the animal shares a technê of storage and release with breeding—painfully slow release in the case of Shakespeare's two equine sonnets.