Grapes, raisins and currents can cause intoxication if ingested by pets. It is important to remember that these are often found in pantry items such as trail mix and granola.

Grapes

Of note, grapevines (all parts, including the leaves) are regarded as toxic to pets.

Signs and symptoms of toxicity: Abdominal pain, vomiting, diarrhea, agitation, shivering, and excessive thirst. These signs can appear within 12 hours of ingestion. Fatal effects (such as kidney failure) may not be seen for up to 3 days after ingestion.

Toxic consumption: The toxicity threshold for dogs is unknown. It is advised that you seek help if even a single grape or raisin is ingested.

References:
– Osweiler, G, et al. (2011). Blackwell’s five-minute veterinary consult clinical companion. Small Animal Toxicology. [Kindle version]. Retrieved from Amazon.com
– The Merck Veterinary Manual. Raisins or Grapes. Available at: http://www.merckmanuals.com/vet/toxicology/food_hazards/raisins_or_grapes.html. Accessed August 31, 2014.