An article in the December issue of The Whole Dog Journal cautions about the danger of dogs ingesting paintballs. Some paintballs contain osmotic laxatives, which can lead to “salt poisoning”. Symptoms include vomiting, disorientation and diarrhea. Osmotic laxatives stimulate the intestines to absorb water from the body, including the brain, which can lead to hemorrhage. They also taste sweet, which makes them even more attractive to dogs. These ingredients include polyethelene glycol, glycerol, and sorbitol. More info can be found in this ASPCA article pdf from 2003.