Human beings have a food pyramid they're supposed to stick to for dietary reasons, although some people have a little bit more on their appetite; rubbers, metals, woods, and more.
These people have a disorder known as Pica, which can exist for a variety of reasons. One of the more common reasons the disorder exists is because the person has a psychological disorder. Others may have the disorder because their body experiences constant mineral deficiency, which leads people to gnaw on things that would provide such minerals.
One French entertainer by the name of Michel Lotito has this disorder, and although most people would suffer severe bodily injury from eating these kinds of things, Lotito ate uncommon items, such as an airplane, a computer, six chandeliers, and even a set of skis over the course of two years. Lotito miraculously didn't suffer any injuries because his body had an unusually thick stomach lining and could handle the additional consumption.
People who suffer from Pica are all different. No two cases of Pica are exactly the same, and each person craves different kinds of items. So could you eat a bus? If you're Lotito, perhaps!