Grape toxicity for dogs is poorly understood in a way that nobody knows why they are toxic to them.
There are stories out there of people who insist that they give their dog the odd grape and their dogs are fine. Some dogs seem to handle that with no problems indeed.
There are people who jumped or fell from great heights and lived too.
One man apparently even survived a 47-floor fall. The question is whether you should go and try to see if you would too. I know I am not going to.
There are dogs that went into kidney failure after eating a single grape. Are you willing to take that chance?
Grapes, raisins, and currants
Grapes, raisins, and currants are toxic to dogs.
I recommend always treating grape/raising ingestion as an emergency.
“If you suspect that your pet has eaten any of these fruits, please contact your veterinarian or Pet Poison Helpline, an animal poison control service, immediately. Do not waste any time. Since there are still many unknowns associated with this poisoning, it is better not to take any chances when it comes to your dog’s health.VCA Hospitals
Any products that contain these fruits in any form can poison your dog. That includes all types of grapes. raisin bread, trail mix, cereals with raisins.
One upside is that grapes and raisins seem to digest slowly and evacuating the stomach can be effective up to several hours after ingestion. However, I advise against trying to deal with this on your own. There are many scenarios when inducing vomiting is a bad plan and there is way more to it.
Call a veterinarian
If your dog ingests grapes or raisins, do not take the chance.
Keep grapes, raisins, and currants away from your dog and if they do manage to eat some, do treat it as an emergency.
Grapes are Toxic to Dogs