How do I find a bad smell (dead animal, maybe) in my house?

That happened to me in a house I used to rent. It was a dead bird in the wall. If it is doing it again it is more than likely a 2nd dead bird. It happened to me 3x. And yes the heat will bring out the smell and it is embarring but short of tearing down the walls there is not much I know of that you can do other than wait it out. Good luck.