At my work, they put out rat poison and one ate it then died in the wall. It was horrible. For months it smelt like a dead body in the front of the store. I'm just glad costumers can't come in and eat.

At a more personal level, I had a zebra fish that decided to jump out of the tank back where the tank was open for the filter. I found her under my dresser after she dried up and was all nasty. I couldn't find her for the longest time though and that smell was terrible.