I have my BPs do it once or twice, and my boa does this once she gets dead prey items without a fight several times. Then I would end up either feeding live or trying to pull the rat away the next time and they go back into battle mode.
On a different note, my psycho pastel will strike at any warm object or movement when he smells a rat, and will chase after his prey items. I'm almost convinced he's a retic hybrid of some sort.