A relative of poison ivy and poison sumac, the cashew contains the same rash-inducing chemicals, known as urushiols, as its kin.

It's interesting to try to imagine how early humans discovered what was edible and what wasn't. Who figured out that when you cooked stinging nettles, the sting would go away completely? How many people had to die before the relative toxicity of wild mushrooms became widely known?

One man's poison ivy is another man's spinach.

I don't know if I cut more poison ivy than brush, ... I had perpetual poison ivy for five years.

It's good soap. It'll get poison ivy off — and ring around the collar. And it won't eat up your hands, no matter what you've heard people say.

The strongest poison ever known / Came from Caesar's laurel crown.