The fact that we're having this discussion at all kind of proves that either English is losing the distinction, or it was never as clear a distinction as people sometimes make it out to be. Either way I'm fine with it because it doesn't seem like a very useful distinction to make in everyday language, and you can sidestep it entirely by using a word like toxic instead.
If I call a snake poisonous, or a frog venomous there is no knowledgeable person that will be confused about what I'm saying. The only people who bring this point up are people who love to be pedantic.
In the way that language is commonly used, yes. People have been using it wrong for so long "jealous" has effectively become synonymous with "envious". Even if I dislike and disagree with it being used this way.
If someone is eating a donut and you say "I'm so jealous [of having the donut]" I'm fairly confident most everyone would understand you mean envious by definition but are using the word jealous to convey that meaning.
Ah, but we can go even further beyond in pedantry. This distinction is only exclusive when we're talking about a living thing. When talking about the substances themselves, one is a subcategory of the other. A venomous snake is not poisonous, but a venomous venom is a poisonous poison.
Yep, and even when talking about living things it's not a clear distinction.
In biology, poison is a substance that causes harm when an organism is exposed to it.
Venom is a poison that enters the body through a sting or bite.
In a bunch of medical fields though, poisons only apply to toxins that are ingested or absorbed through the skin and that definition sometimes carries across to zoology.
Venomous creatures are poisonous by most definitions because venom is a poison. But if the distinction is useful in a medical or zoological context then they're not.
tldr: The pedantry of eg. correcting someone who says a snake is poisonous is totally pointless and mostly wrong.
The toxins are excreted through their skin, and adhere with the oils that keep their skin moist. It is a defense that keeps other animal from eating/touching them. They are not really facilitated to bite as a defense. They pull prey in, and their mouth mostly crushes, and is used to swallow.