Hi everybody!

As you know, some kinds of animals have poisons in their body. For example in their skin, their giblet, etc.

This can halp to survive the kind of animal by killing its carnivore enemies. By why this don't happen for all kinds of animals? Why all of them are not poisonous?

Thanks.

Because it is not always useful. All animals have different ways of protecting themselves. For example some animals have good camouflage, some can run very fast etc.
While having a poison protects the species on a long term by killing the predetors, it does not help an individual's survival. Also, if every animal had some sort of poison in them, we would have to evolve to resist the poison.