Toxicodendron radicans

Leaves of three, let it be. The oil gives an itchy rash that can last two weeks. Wash with soap fast if you brush against it.
The rash is not contagious, and it is not the plant. It is an oil called urushiol, and it can stay active on a jacket for years.
This one is poisonous, which means it hurts you if you touch it or eat it. It cannot chase you, so the rule is simple: look, do not touch.
Always ask a grown-up before you touch any animal or plant. If something bites or stings you, tell an adult right away.
Source: our source list
Read more about the poison ivy at Wikipedia.