Of course they do. We had one died behind a built in cupboard in a dressing room. Right pong and it lasted a while as well. There is no denying natura l causes. If you didn't smell them its probably because you smell worse.
"The fresh stage of decay kicks off about four minutes after death. Once th e heart has stopped beating, the cells in the body are deprived of oxygen. As carbon dioxide and waste products build up, the cells start to break dow n as a result of enzymatic processes - these are known as autolysis. Initia l visual signs of decomposition are minimal, although as autolysis progress es blisters and sloughing of skin may occur.
The second stage of decay occurs as a result of the action of micro-organis ms. The actions of bacteria on the soft tissue of the body produces a varie ty of gases which cause the carcass to become bloated and swell in size. It 's claimed that the body can as much as double in size during this stage of decomposition. The sulfur-containing compounds that the bacteria release a lso cause discolouration of the skin, giving it a yellow-green hue.
As a result of the bloating, the increased pressure causes bodily fluids to be forced out of natural orifices, as well as potentially causing ruptures in the skin. This can cause a formidable odour; at this stage, if insects are able to access the body, flies will lay eggs in exposed orifices, which will in turn hatch into maggots which then devour the flesh.
The third stage is that of active decay. At this stage, the ongoing action of bacteria activity and decomposition leads to the liquefaction of tissues , and the persistence of the strong odour. It is during this stage that the cadaver loses the greatest mass. The final stage, advanced decay, occurs o nce most of the cadaveric material has already decomposed."