My biggest had a similar issue with his live rat this afternoon.

He usually gets it right when I drop it in front of his hide, but the rat had time to crawl in. Nibiru bit him mid tail and lifted his whole hide in order to constrict the rat with most of his back end and the rat butt-up. Once the rat was dead, Nibiru spent 10 minutes going in circles and poking the rat with his nose before re realized he was sitting on top of the rat's head. I almost thought he was going to give up.