My daughter used to take horseback riding lessons. One morning we showed up at the stables. We parked about 50 feet from the entrance and as soon as we opened the door, it hit us, the smell of decomp. A horse had keeled over during the night and the knacker hadn't come yet. My clothes smelled for days. There is absolutely no mistaking the smell of death.
My Dad opened a freezer full of deer meat sometime after the fuse blew on the power to the basement. Great air seal on that freezer ... we didn't smell a thing until he opened it!