DragonkingKyo

true but you forget that sea kings can talk to each other, so they are able to teach others if a species is poisonous to eat. So, it still in the end makes no sense for them to not understand they shouldn't attack them plus those snakes are native to that region and maybe all calm belts meaning the sea kings should have developed an instinct to avoid them like want happens to most creature that live around poisonous animals for long periods of time.