Holly berries are indeed poisonous to dogs. The plant contains toxic chemicals such as saponins, methylxanthines, and cyanogens that affect dogs if ingested. While the toxicity is generally considered low, eating holly berries can cause symptoms like vomiting, diarrhea, drooling, loss of appetite, and lethargy. Ingesting the spiky leaves can also cause mouth injuries. Although holly poisoning is rarely fatal, severe cases can lead to dehydration and, in very rare instances, collapse or seizures. Puppies, older dogs, and dogs with existing health issues are more vulnerable to severe effects. If a dog ingests holly, it is advised to contact a veterinarian promptly for guidance and possible treatment.

In summary:

• Holly berries are poisonous to dogs.
• Symptoms include gastrointestinal upset and mouth irritation.
• It is usually not fatal but can cause serious discomfort and dehydration.
• Veterinary advice should be sought if ingestion is suspected.

Therefore, it is important to keep holly plants and berries out of reach of dogs to prevent accidental poisoning. Artificial holly decorations can be a safer alternative during the holiday season.