The red berries of Holly plants, which are very appealing to cats, are poisonousPlants are a great addition to homes and offices, but it’s important to know whether your plants are dangerous to children, pets, or even adults. Some plants contain chemicals such as oxalates, solanine, glycosides, or alkaloid lycorine that may cause vomiting, nausea, diarrhea, swelling and redness of the mouth, throat, and lips, and trouble breathing. Touching parts of certain plants, especially the sap, may cause various skin irritations. The weight and age of the human or pet involved, and the part and amount of plant eaten determine how severe the reaction to the toxins will be. Although plants may be listed as non-toxic, they can still cause individual allergic reactions. If there is any question after a houseplant has been ingested or touched immediately call the Poison Control Center 1-800-222-1222 The Handbook of Poisonous and Injurious Plants [Paperback]is an excellent reference to keep around if you have young children and pets.. If your cat eats these attractive red berries, he may experience vomiting and diarrhea. You should contact your vet immediately if this occurs.