A snake swallowing it's food tail or end first can be deadly!!!
Just KIDDING!!!
It's absolutely fine and it happens quite often. Next time, don't even bother trying to take the mouse away or change it's position, the snake WILL figure it out and eventually get it down.
If it's too big to get down the hatch, the snake will "spit" it out and start over. A couple of mine are very slow eaters in that respect. They'll start eating it then spit it out and start over again more than once for one item. Aside from taking forever to actually swallow the food item, nothing else will happen.
Pixie