I don't know about hamsters and small chicks, but I'm pretty sure a BP wouldn't get big enough to eat a guinea pig, and they would never really come into contact with fish that much in their natural habitat, so I don't believe they've ever thought of that either.

About them eating ferrets... (This is a bit of a pet peeve of mine as you may notice shorty) Ferrets are not rodents, and have actually been known to kill snakes for food in their habitat from time to time. They don't smell like rodents, and they don't give off the same prey signals as a ball python's natural prey items would because they aren't really prey animals. I'm near 100% sure a ball python would not eat a ferret, whether live or pre-killed.