I've seen this to. It looks to me that the snake is taking a quick breather after eating. Like he has just become to lethargic to reset his jaw. The way I see it feeding for a snake is a physically exerting process and some times when they are done they are just exhausted so resetting there jaw then becomes second priority to taking a quick breather and finding shelter. Once again I'm not positive that this is the reason for this behavior. Just a theory. I've seen it a couple of times and that always seems to be what it looks like to me. :/