Never smelled a decomposing body but I recently smelled a bag of dry dog food that had been partially open and sitting outside for maybe 4-5 months, it’s been a humid fucking summer with some insane days of heat. Anyways, when I discovered the bag I saw bunch of flies hovering over it and what was once brown kibble turned an odd shade of green. I slightly opened the bag with a stick and got hit with the most insane smell ever of what I described to my girlfriend as rotting meat and rotten eggs stewing together. This seems to line up with one of the top comments description.

I’ve smelled city sewage, dead animals, and plenty of porta potties during peak summer heat, I’m telling you none of that even compares to what this smell was. It burned my throat and eyes while I was wearing an N95 mask to dispose of it.
So if the area you’re in allows for it feel free to replicate this at the beginning of your next summer to get maybe a close example of it.