Describe your setup - more info please.

Might be "snapping" at the "brightest" heat source. You use lamps of any sort? Have your hand anywhere near where she's snapping? How do you mean "when the mouse is on its back"?

Starting the swallow from the back or side initially is hardly unusual though. One of ours seems to have no problems swallowing backwards - the rest occasionally nose around trying to get everything lined up just right after oddly aligned attempts.

In short nothing wrong.