It depends on the conditions where the body is. For example, a फ्रोज़न body will decompose much और slowly than one in a hot and humid environment. But basically, once life stops, the bacteria w/n our bodies starts to consume the flesh. If unattended, bugs come to eat the corpse, as will any other wildlife. There are lots of पुस्तकें out there that describe the process of decomposition; off the चोटी, शीर्ष of my head, Mary Roach's "Stiff" is a decent place to start. She's a very good science writer.
