My boa tried to do that once... dumby. Not sure if the rat was so frozen in fear and was just that still or my snake was having a serious lapse in judgement, haha. She found out pretty darn quick that trying to slowly grab a live rat's behind wasn't going to work. This was right after she already ate one rat, so maybe her feeding response wasn't that great anymore. I have started feeding her one rat in a feeding now, if she's going to pull that move, she'll just end up getting bit. Luckily she recovered fast enough that it ended in a tight, happy hug.
My ball has always had a great feeding response, she has always been alert and ready to strike as soon as she smells the rat.