Be quiet or the snake eats you

It's equally valued, if someone says a snake is not poisonous they are usually meaning that it's not venomous, as there's very few contexts where people are worried about the risks of eating a snake, and very few are poisonous.

So yes conversationally the rat is right as he knows the concept is mis implied.

However, it's also worth pointing out that, the story doesn't tell us whether the snake is venomous at all. He's drawn with fangs so, maybe, but it's entirely a moot point because snakes don't need venom to kill a mouse.

So we shouldn't feed the troll....hmm...

Also even if it isn't venomous, it still eats critters.

Well, actually armphdgg

Ackshully, we're very nutritious

What annoys me about people correcting this is that it's never been incorrect. Poisonous has been used to mean "having a bite or sting that injects poison" since forever.

I think most (but not all) native speakers either intuitively know the difference and use the right one usually, or they hear the right one used in each specific context enough to just associate them - like how we don't usually think about what name to use for a group of animals (herd, flock, just "group", etc.) because we've heard other people call each kind a certain group name most of the time. Unless it's a funny one like a murder of crows. So it's not even a matter of being petty, just being exposed to it enough

As for how much value it adds to the language, we keep words for almost anything, so the bar is rather low and like you point out, some creatures could be either or both.

For example, some puffer fish have sharp spines that one could assume are venomous, but they aren't, the fish are only poisonous, which affects how dangerous they are to be near (not so bad). Meanwhile yes, some snakes/frogs are both venomous and poisonous.

Yeah that surprised me when I learned giftig in German and that it had both meanings. The distinction feels a lot more like an artificial quirk of English now.

Both to eat and ones that leak it when attacked!

I think at least some other languages have the distinction, but only in use in medical contexts where it might actually matter. English is also the only one I know that does this in lay-speech and has a group of people trying to push it further (not that it hurts anything, I suppose, to be more accurate).

Yeah this is one of those things that pedants latched onto and isn't even true in all contexts

Neat!

But it isn't poison. It's venom.