In my previous home we had an outbuilding which DH converted into my quilt studio. I had to persuade him to put in a half (maybe a quarter bath) and it made a great guest room. It had electric heat as well. Everything was wonderful until the mice moved in. Since mice don't have bones, just cartilage, they can get almost two dimensional to get where they want to be. They not only used my stash as a communal toilet they loved to use batting for that purpose as well as nesting material. We set mouse traps in the stinking attic where they seemed to be nesting and pooping the most but it was so shallow that we could only reach a small part if it through the little trap door. Then I was treated to the scent of decomposing mice. Then one day a very long rat snake was seen slithering up the down spout and apparently found a way in. NO MORE MICE!! YEAH FOR THE SNAKE!! With the help of two springer spaniels the closet mice were dispatched when I emptied out the boxes of fabric and batting. Eventually we and time got the stink cleared up. A year or two later I saw my friend making his way up the downspout with another, smaller one of his kind. OH GOOD I thought. He's brought home a bride.
The snakes were very discreet (read that shy), quiet and utterly noiseless. I am ignorant of snake toiletry habits but never smelled anything from then and no house guest ever knew they were up there. I'd had one guest come to in the night with a mouse running across her face before my wonderful tenant moved in.
Rattle snakes give you fair warning. It's the copperheads around here that I fear.