Grapes are poisonous to dogs. They contain toxic substances, likely including tartaric acid, that can cause acute kidney failure, which can be fatal. This toxicity affects dogs differently; some may be severely impacted by even a small amount, while others might not react as strongly. Because of this unpredictability and the potential severity of the reaction, dogs should never be given grapes or raisins in any amount. Additionally, grapes pose a choking hazard for dogs due to their size and shape. If a dog consumes grapes or raisins, prompt veterinary treatment is critical to prevent serious health consequences or death.