I have shared the underside of my mobile home with a huge ratsnake for several years. She eats mice and rats, but still leaves enough behind for the cat to hunt. Only time I see her is when she comes out to sun herself on my driveway on cooler but sunny days.
She's actually gotten quite tame with me and puts up with me doing things like shoving her out of the way with my foot. Rat snakes are constrictors and not venomous (in fact, they, especially the fancy colored ones, are popular pets), but like most snakes, have a mouth full of sharp, back-curved teeth that makes a bite an unpleasant experience.