And you can never predict the mindset of an irate dog owner who returns to a smashed car window and a circle of strangers calling him a villain.
"If you break a window, you are suggesting the owner has behaved in a neglectful or even cold manner," he says. "A lot of people bristle at that suggestion."
So, you might get sued - or worse.
"Keep in mind the possibility that someone might not only be sued by the dog's owner, but might be prosecuted by law enforcement and the district attorney for, say, vandalism or property damage," Pierce says. "It would be politically unlikely for a prosecutor to invest resources in a case like that. But it's possible - especially if the person didn't take the kinds of precautions that I described."
But even outside of those Good Samaritan states, there's a good chance the court will side with you, according to Pierce.
"It's possible that a court would consider that a person who behaved in that manner acted rationally and reasonably," he says. "And that the value of the animal's life is rightly to be privileged above the cost of replacing the window."