Is there an animal which, when eaten by other animal, poisons the predator and gets out of it's stomach?
The closest I can think of with that hint is a Middle Eastern beetle that hunts frogs and other amphibians:


  In almost 400 face-offs, the amphibians only managed to get the larvae in their mouths seven times. Even then, they soon spat out the larvae, which quickly turned on them (first video below). One toad even managed to swallow a larva, which moved inside its stomach for two hours. For some reason, the toad eventually regurgitated its catch, and the larva, apparently unharmed, killed and ate the animal that had just eaten it (second video below).


However, it's only a pseudo-fit to the clue. The beetle doesn't hunt American bullfrogs, but ones native to its area of the world.