When we had septic, being a city girl, I waited with horror for something bad to happen but have a sewer now. My SIL got a terrible smell, called the gas company thinking it a leak, what they found was a mouse crawled (???!!) up in her oven door (How??? Who would thunk it possible???) insulation, couldn't get out, died and stunk up the place, and Gas guys did not appear surprised. Sniff there.