马钱子（马钱 (Strychnos nux vomica)）树的种子；又称“毒坚果”

Photograph of seeds from strychnine (Stychnos nux vomica) tree. These seeds contain about 1.5% strychnine, a highly poisonous and intensely bitter alkaloid. Although strychnine has no recommended medicinal uses, some traditional Chinese herbal veterinary medicine remedies and homeopathic substances contain herbal strychnine in undisclosed amounts, putting veterinary patients at risk.