Giant Hogweed . Giant hogweed is an invasive plant, which contains toxins that can cause severe burns and scarring. Dangerous to both humans and their pets, the stems and leaves of the plant can lead to nasty skin burns and blisters while the toxin is in a higher concentrate within the sap which is released if the plant is snapped or broken.
https://www.lynnnews.co.uk/lifestyle/9-plants-and-insects-that-can-harm-your-dog-9255673/