If you live in an old house, then chances are you're going to have a pest problem. The siding on old houses certainly isn't up to par with newer designs and cracks in the siding and holes along the baseboard can allow rodents to get into the house itself. Perhaps you've heard some scraping noises in the walls or in the attic, but haven't thought much of it. But then one morning you wake up to a nauseating smell in the house.
This smell is most likely from the decaying body of a dead mouse. However, if you own a gas stove or use natural gas/propane for your heating needs, then it is advisable that you call your gas company. Although natural gas is odorless, it is infused with an additive that smells like a cross between rotting eggs and rotting flesh. That way if you have a gas leak, you'll be able to detect it before it potentially threatens your home or your family. Thus, it is a good idea to call your gas company and have them verify that in fact you have something dead in your house and not a gas leak. Paying fifty bucks for an in-home visit from the gasman is better than having your house explode if you neglect a gas leak.