According to the Pet Poison Helpline, “Certain types of yuletide plants (e.g., mistletoe, rosemary, holly berries, etc.) can be toxic to pets. Varieties of English, Japanese, and Chinese Holly contain toxic saponins. When Christmas or English holly is ingested, it can result in severe gastrointestinal upset (e.g., vomiting, diarrhea) thanks to the spiny leaves and the potentially toxic substances (including saponins, methylxanthines, and cyanogens). If ingested, most pets lip smack, drool, and head shake excessively due to the mechanical injury from the spiny leaves.”
To be on the safe side, keep your yuletide plants out of reach of your dogs and cats during the holidays. If you suspect your pet has ingested holly, contact your veterinarian or Pet Poison Helpline for treatment recommendations.