Here is my dead animal odor story. Skip if you want to:
Way back when I was married, my husband and I took kids for a 3-week vacation. When we got back, found out that our kids best friends in the neighborhood (ages 10 and 11) had used key we left with their parents to go in and read Playboy books my ex had stuffed in his closet, plus they had raided gumball machine and candy cupboard. Parents told us about it, and punished them, as well as closed and locked back doorwall kids had left partly open for a couple of days.
Soon afterwards, we had a bad smell in the downstairs and searched everywhere to no avail. Finally smell went away, but a few years later, my then older teen son and his best friend helped me move furniture for the carpet layers that were coming. Behind and slightly under a big, two-piece china cabinet, kids discovered the desiccated body of a dead squirrel, which no doubt was the cause of our smell that year. Kids got freaked out because you could see from one eye socket through to the other, which was a good punishment since friend was one of the house-breakers several years before. Apparently, squirrel came in the open doorwall and died, but since he was behind and under the china cabinet, we never found him.
So, I always consider a dead animal as the cause of a bad smell, especially since I have had a racoon and several other small critters sneak into my RV, planning on setting up housekeeping in my basement storage areas.