Dogs have been our faithful companions for thousands of years, but there are still so many mysteries associated with the furry love machines. What are they thinking about? Do they love us as much as we love them? Perhaps most pressingly, what happens if they eat a grape?

The answer to that last question, at least, is straightforward, if horrifying. Since pups have long been the off-brand Roombas of the human domicile, it might shock you to learn that their systems, for whatever reason, just weren’t built to handle what your fun, intermittently divorced aunt probably referred to as “pre-wine” at some point. Consuming the fruit can lead to pretty severe consequences for man’s best friend.

In fact, the reaction that a dog can suffer from grape ingestion is so severe, it even has its own name: “grape toxicity.” According to the nutritionists at Purina, nobody’s quite sure exactly what causes canines’ violent physical response to grapes. Whatever it is, things get messy fast. On the low end of the spectrum, your dog could experience run of the mill symptoms like a tummy ache, vomiting, and diarrhea. Depending on the seriousness of the reaction, things can ramp up fast to polyuria (which is a fancy way of saying “peeing too much”), dehydration, and even kidney failure. And yes, for any letter-of-the-law types out there, this all goes for raisins, too. The craziest part is that, since we don’t know what chemical in grapes causes this, any amount of the fruit can prove potentially lethal.

So what do you do if this situation arises? The folks at PetMD recommend that you induce vomiting using a small dose of hydrogen peroxide if the pupper isn’t unconscious or having trouble breathing and hasn’t blown chunks already. In any case, keep in mind that yes, this is a medical emergency, and it’s imperative that you get your buddy to the vet right away.

And there you have it. The Achilles’ heel you never knew Cujo had: the California Raisins.