What's the difference between poison and venom?

We all know to be wary of toxic encounters with the natural world, whether it's watching out for venomous snakes or not eating poisonous berries. But while both of those threats involve toxins, we call the berries "poisonous" and the snakes "venomous."

The terms "venom" and "poison" are not interchangeable. So what is the difference between poison and venom? The distinction is more about style than substance.

Put simply, venom is injected directly by an animal, whereas poison is delivered passively, such as by being touched or ingested.

"If you bite it and you get sick, it's poisonous. If it bites or stings you and you get sick, then it's venomous," said Jason Strickland, a biologist at the University of South Alabama who studies venom.

Related: 30 unusual poisonous animals

In a research article published in 2013 in the journal Biological Reviews, scientists proposed a third category of natural toxins: the "toxungens." Toxungens are actively sprayed or hurled toward their victim without an injection. For example, spitting cobras can spew toxins from their fangs.

But poison and venom don't always work the same way. For example, venom won't necessarily hurt someone unless it enters the bloodstream, according to the University of Florida Department of Wildlife Ecology and Conservation.

No matter how they're delivered, these toxic chemicals are highly effective weapons in the evolutionary arms race between predator and prey. And in some cases, a single animal can employ its toxins on both offense and defense.

Spitting cobras, like the black-necked spitting cobra (Naja nigricollis) and the Philippine cobra (Naja philippinensis), spit out toxins in self-defense when confronting a threat and inject venom into their prey to hunt, making them both toxungenous and venomous creatures. Sometimes, two different methods are used for the same purpose. The fire salamander (Salamandra salamandra) defends itself with toxins on its skin and toxins squirted from its eyes, making it both toxungenous and poisonous.