bodies decompose because of microorganisms eating us! We’re no longer making new cells to replace the old, and we no longer have antibodies to fight anything off, so when the tiny tiny organisms start to eat us up there’s not much we can do about it anymore. At this point there might be flies laying maggots in us, which will also start to eat us up too (eww! have you ever seen maggots or fly eggs? they look like little grains of rice lying about). The bad smells are probably due to a number of reasons – it could be waste products from the organisms that are eating us up (translation: poo) or even our own poo, once our gut has ruptured and things are leaking out of it.
This is gross, and I haven’t even eaten lunch yet. Halp. lol.