Yes, Swiss cheese plants are toxic to humans and common household pets like cats and dogs. The plant’s sap contains calcium oxalate, which is toxic if ingested. Signs of poisoning include mouth burning, nausea, vomiting, and diarrhea. The plant’s sap can also irritate skin, so it’s important to wear gloves when pruning Monsteras. When grown outdoors, Monsteras may produce fruit, which is edible, but only when ripened.