The only two times I've ever had a ball spit out a partially swallowed food item was when it was a bit too large. Most of the time, if they think it is too big, they won't even bother to try. But now and then an especially hungry one might snag a meal that turns out a little bigger than it thought. I've never had one swallow the prey then regurge, but I have had them get the head and neck down, and realize the shoulders were too big and spit the prey back out.

Gale