That is surprising, did he never take a bite? In my experience as soon as claw, tooth or talon offer the snake discomfort they will do what is necessary to subdue that prey before continuing. Seems like swallowing a big, living rat head first would incur some nasty retribution from the rodent which would in turn trigger that snake to react accordingly. Many snakes will not bother to subdue helpless prey and swallow it alive. It doesn't get much more helpless than a pinky rat.