Is it possible the rat got stuck on something (like the bedding or hide)? I know when that happens to my snakes, they will usually give up and leave it. This happened the other day with my spider, where the mouse got stuck under his paper towel bedding. He appeared very confused and picked at it for a minute, before looking at me like "a little help, mom?" I reached in and removed the mouse from the paper, and he immediately snatched it off the tongs - and proceeded to eat after a second of fake coiling. If that's not the case, it could be that the prey was too big... or just a random occurrence, as Mona does occasionally with a rat for unknown reasons. Snakes are weird sometimes, LOL.