We live and learn - hopefully. Sometimes at the expense of our precious animals.
Some people have just been lucky so far, that their snakes have managed to escape being bitten and badly injured by the rat/whatever.
What's the problem just killing the prey first? Or feeding F/T items? I agree with Merlin that the F/T has been proven to be perfectly good nutrition wise.
I have seen awful injuries to snakes caused by their intended prey trying to defend itself in the best way it knows - CRUNCH.