Hi,
Did you weigh the mouse prior to feeding? A general rule of thumb to use (which you may already know, but I’ll mention for those who don’t) is to avoid feeding prey that has more girth than the snake at its fattest part.
You can also view a mouse/rat guide, including weights and relations,
by clicking here.
If the size/weight was not an issue, than I’d hazard to guess that the reason it took so long for him to get it down was because it was backwards. As I’m sure you’ve observed, when swallowing prey head-first the arms and legs naturally fold down at its sides, thus making a much easier swallow. When swallowing backwards it can be much easier for limbs to stick out in odd places, thus forcing the snake to reposition the morsel in addition to using more muscles to force it down.
But as long as he got it in, that’s what counts!
When snakes swallow food whole their breathing tube, called a glottis, extends out of their lower mouth and bends slightly down. That way they can still breath while taking all the time they want to swallow.
Nice resolution on the second pict!