So about a week ago my wife and I hear this scratching sound coming from the walls. Oh great, we’ve got a mouse (or something similar). Here it is one week later and the scratching has stopped but there is this aweful smell of death. So I put two and two together and assume our little friend didn’t make it. What can I do, besides burning scented candles 24-7, to get rid of this smell? I really don’t want to start ripping holes in my wall.
That happend to me once about 2 years ago. With time the smell should fade. I wouldn’t reccommend tearing up the walls, because chances are you won’t find the vermin. I reccomend Ozium spray, it gets rid of the bad smell pretty well.
Had a similar thing happen to me. I live in an older (1860s) home, which is apparently perferated like swiss compared to the modern ones around, and we occasionally get (or notice, they’re probably always here - don’t tell my wife that though) mice.
The bad news is that he’ll stink for a long time unless you have a good decomposer in your wall (like insects or bacteria - not too likely), so you might want to find the little guy.
I’d try to find him (by smell? where you heard scratching? holes in the wall?) on your own. Or you could call an exterminator to do so, he’ll probably charge you the low, low price of only $100 (if you’re lucky).
It is probably a little larger than a mouse, as these tend to simply dessicate without making too much smell (at least in the dry environment of a house) - most likely you have a rat or a bird in there, but the smell will fade away as it dries out.
SkyTiger is right on the money - unless you have walls with easily removable panels (not common in houses, but I dealt with a dead rat problem in the cavity wall of an industrial building once), opening the wall is going to be massive hassle and you probably won’t find the carcass, as the odour could be travelling a bit.
Burning a few matches, which contain sulphur, will help mask/kill the smell temporairily.
Get some sulphur powder and burn in a fireproof dish, bottom of upturned can, etc.
Not too much at any one time as the products of combustion, in quantity, are noxious.
Wait for the carcase to dehydrate.
We had a bird’s nest in our bedroom wall, which is located on the second floor. It really stunk, and I had no choice but to tear out the drywall. I then took the nest (along with three baby birds) and threw it out the window. The outside hole is now plugged up…
Just wanted to share the resolution to my odor problem. After waiting and waiting for the smell to go away (it got worse and worse), I finally called a professional “odor control specialist”. He was able to get a general location of the vile smell using his sniffer. By the type of smell he was positive it was some type of rodent. Next he removed the floor board and cut through the dry wall between the studs he thought it might be located. A couple of pokes with the hook and bing two ripe, rotting mice appear. He then sprayed an odor eliminating spray and put the floor board back on. Problem, hopefully, solved (though I need to replace some drywall). Well worth the money (about $100).
Morale of the story, a few mouse traps on the front end can save you a bundle of hassle and money in the long run!
Hope this may help someone else in a similar situation! 
If a good odor-killing spray doesn’t work, take your mind off the situation by sitting down with a good book.
I recommend Poe’s “The Cask of Amontillado”.