Decomposition happens in stages with the help of nature
Whilst not the most pleasant thing to think about, decomposition begins immediately after death. Cell membranes rupture as the body is unable to remove unwanted waste materials. The skin will discolour and become loose and the body swells with unexpelled gasses. Putrification would have been occurring and liquids forming. The body would look bloated and the skin may have split in places.
Flies and other insects that find the body and begin laying their eggs. The Blowfly can smell death from a mile and a half away. Rodents and other scavengers may have had a feast or two depending on the location, this is sometimes made obvious by the teeth marks on the bones and remaining flesh.
Near the end of the first week of decomposition, maggots would have begun to hatch and eat the body. And you would be aware of an accompanying disgusting smell emanating from the corpse that can linger long after the body has been removed.
Eventually, the maggots would leave the body to find somewhere to pupate. And looking at the stage of life the maggots are at can give an indicator of how long the body has been deceased. Although the climate is a factor in this calculation.
As liquids begin to be released through the bodies orifices, the organs, muscles, and skin are liquifying.
In the end, all that would be left would be dried skin, bones and cartilage.
Temperature, location, and other factors can all have an effect on when decomposition starts and how quickly it progresses. But often it is the smell that first indicates the presence of a body.
“A dead body, specifically a human corpse has a rank and pungent smell mixed with a tinge of sickening sweetness. Imagine a rotting piece of meat with a couple drops of cheap perfume and you’re halfway to understanding what a human corpse smells like.” – Courtney, Thought Catalog