Black calla is mildly to severely toxic to dogs, depending on how much is ingested. Usually its strong distastefulness prevents dogs from consuming significant quantities - however, if you see symptoms of severe poisoning, you should seek immediate veterinary treatment. All parts of the plant contain calcium oxalate, which causes extreme irritation when eaten. A red or swollen mouth or throat, coupled with a burning sensation, difficulty swallowing, and a loss of appetite are all indicative of black calla consumption. Vomiting and diarrhea are also common. In extreme cases, when large quantities of the plant have been consumed, organ failure, coma, and death may occur.