I would also think it depends on the snake. Most of mine seem to know as soon as I take a rat out of the freezer and start looking for a meal. I schedule my rat cleaning days on feeding day and mid week and don't handle my snakes when I know I reek of rodent just in case. My boas and short tails I think would be asking to get bit keeping a rat in their room, the ball python and hognose probably not so much.