Added to the opinions mentioned above I would like to venture another viewpoint...
(Please read in the voice of Richard Attenborough)
The grain-eating human supertribes that roam the countries in Europe and North America have developed a habit unseen anywhere else in the animal world. They actually create most of their food themselves whereby they take the utmost care that it bares no resembles whatsoever to any natural origins. Human grain eaters seem to appreciate food most when it has fantastic shapes and properties, as can be seen observing human children eating cereal. One of the explanations is that as a result of having no natural enemies, and having developed themselves in every ecological niche possible, they can actually take the time to play with food. Playfulness, by the way, is a very important skill in their young, adults are discouraged to display this behaviour.
The more likely explanation is that the grain eater tends to fashion his territory to his liking and that food is just a part of this. Grain eaters can be seen erecting barriers, living quarters, communal pathways and even influencing nature itself to create a predictable surrounding in which the graineater feels safe. In that the grain eater differs from most other animals who will just mark their territory using urine.
It seems that fashioning and restyling food is a next level in the development of the supertribes.