Well, if snake doesn't live in nature anymore, it is actually perfectly normal to feed it with rodents.. If a man takes any animal (including snakes) under his roof, he's obligated to care of them and feed them, and as snakes eat mouses/rats, it is just a feeding, a circle of life.
Btw. if you're not a stric vegetarian or vegan, better think of WHAT (OR WHOM) YOU EAT