Hello,
It happened to me one time; the rat was scared (I think) and wasn't moving... So my female slowly came closer and tried to swallow it... Eventually, the rat realized that, and tried to flee, but the BP was faster, and finally constricted it.
One other time, she even swallowed a live rat, knocked out, but it was still breathing, it even moved, like a chocking reflex. That was a bad one… Nasty girl. No need to mention that I have a pretty intense feeding response with her.