The short answer is yes. The sap of a Christmas cactus contains small amounts of oxalic acid, which can be toxic to cats if ingested. Cats are particularly sensitive to this type of toxin, so it's best to keep Christmas cactus out of their reach and to monitor them closely if they do come into contact with the plant. Symptoms of Christmas cactus poisoning in cats can include excessive drooling, vomiting, diarrhea, lethargy, and difficulty breathing. If you suspect your cat has ingested any part of a Christmas cactus, contact your veterinarian immediately for advice.