Hydrus

The Hydrus is a creature that lives in the River Nile, and is the enemy of the crocodile. When it sees a crocodile sleeping on the shore with its mouth open, it rolls in the mud, making it easier to slide into the crocodiles mouth, and allowing the crocodile to swallow it alive. The Hydrus eats its way out through the crocodiles stomach, killing the crocodile and escaping. In medieval Christian tradition, this is allegorical of the resurrection of Christ (the Hydrus), bursting free from Hell (the crocodile).