I have never smelled a human corpse, but a neighbor was found dead in a trailer after about a week and they said the smell was so bad, they were going to have to destroy the trailer. This was after they kept the windows open for about two weeks.
For the sake of your request BBM, I can give you some examples of things I have smelled.
I guess someone could try to say it was a rattlesnake in the trunk. It smells like something dead. I've smelled them and it's a terrible smell. And, there was that dead one that Kronk had.
Dead animals can smell.
I've had to pull a shot dead deer out of a pond and it was enough to make me gag and gag.
A dead dog with vultures attacking it smells bad when the wind blows right.
I had a baby goat who was killed by a billy and by the time I got home that afternoon, it was already decomposing with maggots and blowflies, etc. all over the openings (eyes, nose, mouth, rectum). It smelled, but I don't remember an overwhelming smell.
Even the tadpoles I vacuumed out of the pole had a stench when they die out in the sun.
I can't remember exactly what HLee said when he looked into the trunk to examine it, but he knew it right off. Maybe someone remembers the video where IIRC he jerked his head back when he got a whiff.
Even after ICA and the A's tried their best to clean out all the evidence, I have no doubt that it was Caylee's decomposing body that was in the trunk of the car, NONE WHATSOEVER.