These are the berries of Poison Ivy. Leaves, flowers and berries, in fact, every part of this plant can cause an allergic reaction amongst those who are susceptible to this plant. I used to be immune and could walk with impunity around it, never reacted. But suddenly, this past summer, things changed and I got a severe reaction, to the point my leg and foot swelled up and I had to go on antibiotics and prednisone :-( Apparently one's immunity can change almost from one day to the next, and had I known that, I would have been more careful. I am now! It is not an experience I'd care to repeat.