Another thing worth remembering, too, is the fact that in some communities, discharging a paintball gun might be illegal. My sister in law lives in a town where they can send ya up the river even for shooting off a slingshot.
A goodly number of pet owners have IQ's scarcely higher than their animals and would be incensed that ya would have the audacity to plug their little darlings with a paintball. The fact that they were being inconsiderate jerks by (often illegally) letting their pets run loose would never occur to them. And curiously, the law might come down harder on you than on them.