Acorns are toxic to dogs, probably because of the tannic acid they contain. Eating acorns can damage a dog's liver and kidneys. Eating oak leaves and drinking water in which acorns or oak leaves have soaked can also poison a dog.
Many common plants are poisonous to dogs. Outdoors, dogs sometimes eat daffodils, bluebells, ivy, mushrooms or horse chestnuts, which can all cause vomiting and diarrhea. Bluebells can also affect heart function, while certain mushrooms can cause liver disease or neurological symptoms. Other potentially dangerous plants include house plants such as aloe, dieffenbachia, golden pothos, heartleaf philodendron and variegated philodendron. Seasonal decorative plants such as poinsettias and mistletoe are also poisonous to dogs.