Snakes sometimes do funny things with their food. My Red Tail will strike and constrict the daylights out of it's food and then just leave it there after he's sure he's killed it. But, when I try to remove the dead rat, he shoots over and immediately coils around it again and refuses to let me take it out. It's like his teddy bear or something..I dunno.
My point is, each snake attacks and eats it's prey the way they want to, not the way we think they should. As cruel as it may seem to watch a snake do that to live prey, it's the law of nature. Just give him some time and he'll adjust to feeding.